GLL1K

Manual

Thank you for your purchase of a Boscoe Music GLL1K Wiring Harness!

The GLL1K is a complete replacement wiring harness for the G&L L•1000 bass. It recreates the distinctive passive electronics used in the L•1000 while replacing much of the original point-to-point wiring with compact PCBs, screw terminals, and prewired components for easier installation and future service.

The harness includes the complete Volume, Treble, and Bass control network, output jack, pickup-mode switch, grounding hardware as required for the selected version, and the resistors and capacitors used by the circuit.

No battery or external power is required. The GLL1K is a completely passive wiring harness.

Available GLL1K Versions

The GLL1K is available in four versions so that the harness can be matched to both the instrument construction and available cavity space.

Through-Body — Full-Size Potentiometers

18mm shaft length
9.5mm threaded bushing length
24mm-wide potentiometer bodies
Includes potentiometer grounding strap
Best suited to through-body installations with enough cavity space for full-size controls

This version is generally recommended for G&L Fullerton Deluxe instruments and other rear-routed G&L bodies designed around full-size potentiometers.

Through-Body — Mini Potentiometers

18mm shaft length
9.5mm threaded bushing length
16mm-wide potentiometer bodies
Includes potentiometer grounding strap
Better suited to compact or unusually shaped rear-routed control cavities

This version is a good choice when adapting the GLL1K to a non-G&L bass body or any installation where full-size controls may not fit comfortably.

Control Plate — Full-Size Potentiometers

15mm shaft length
6.5mm threaded bushing length
24mm-wide potentiometer bodies
Intended for metal control-plate installations
Does not include the separate through-body grounding strap

This version is generally recommended for G&L CLF Research models using a metal control plate when there is adequate room for full-size controls.

Control Plate — Mini Potentiometers

15mm shaft length
6.5mm threaded bushing length
16mm-wide potentiometer bodies
Intended for metal control-plate installations
Does not include the separate through-body grounding strap

This version is useful when fitting the harness into a compact control cavity or adapting the system to a non-G&L instrument.

Full-Size vs. Mini Potentiometers

The electrical values and tapers are the same between the full-size and mini versions.

Both versions sound the same.

The choice is primarily mechanical.

Boscoe Music generally recommends:

24mm full-size potentiometers — when installing the GLL1K into a G&L body designed for full-size controls.

16mm mini potentiometers — when installing the GLL1K into another type of bass body or any cavity where space is limited.

The full-size controls provide a larger mechanical package, while the mini controls provide more installation flexibility.

Choose the version that best matches the available cavity space and mounting thickness.

Kit Contents

Every GLL1K Wiring Harness includes:

prewired Volume potentiometer
prewired Treble potentiometer
prewired Bass potentiometer
prewired output jack
three-position ON-ON-ON Pickup Mode switch
PCB mounted directly to the Pickup Mode switch
central wiring PCB with screw terminals
passive tone-network capacitors and resistor
three push-on knobs
mini screwdriver
self-adhesive neoprene insulating pad
associated hookup wiring

All versions use 6mm knurled potentiometer shafts.

The through-body versions also include the preassembled potentiometer grounding strap with ring terminals.

The control-plate versions do not include the separate grounding strap because the metal control plate normally provides the electrical grounding between the potentiometer bodies.

What the GLL1K Replaces

The GLL1K is intended to replace the complete control harness of a G&L L•1000-style instrument.

The central PCB replaces much of the component-to-component wiring found in the original L•1000 harness and provides clearly identified connection points for the controls and switch network.

The Pickup Mode switch PCB replaces the more complicated point-to-point wiring normally required to create the classic L•1000 pickup modes.

About the L•1000 Electronics

The G&L L•1000 is unusual because it achieves a very wide range of sounds using an entirely passive circuit.

A typical L•1000 has:

one G&L Magnetic Field Design humbucker
Volume
passive Treble cut
passive Bass cut
three-position Pickup Mode switch

The Pickup Mode switch provides:

Parallel
Single Coil
OMG

The Treble and Bass controls are both passive cut controls. They do not electronically boost frequencies and require no battery.

With both tone controls fully open, the pickup retains the greatest amount of its natural frequency range. Turning either control down progressively removes part of that range.

Control Values

The GLL1K uses the control values associated with the vintage L•1000 circuit:

Volume — 250kΩ audio taper

Treble — 250kΩ audio taper

Bass — 1MΩ reverse-audio taper

The GLL1K central PCB contains the passive tone-network capacitors and the 6.8kΩ resistor used in the circuit version reproduced by Boscoe Music.

Because the capacitors and resistor are mounted on the central PCB, no separate tone-network components need to be soldered directly to the potentiometers.

Before You Begin

Before removing the original electronics, take several clear photographs of the existing wiring.

Photograph:

pickup wires
Pickup Mode switch
Volume potentiometer
Treble potentiometer
Bass potentiometer
output jack
bridge ground
control plate or cavity shielding
and any existing ground connections

Older G&L instruments may have been repaired or modified during their lifetime, and factory wiring may differ from later examples.

Do not rely on wire color alone unless you have verified the pickup configuration.

If possible, label the original pickup wires before disconnecting them.

Disconnect the instrument cable before beginning installation.

Work on the instrument on a padded, stable surface.

Confirm the Correct Harness Version

Before removing the old harness completely, confirm that the GLL1K version you purchased matches the installation.

For a rear-routed or through-body instrument, the 18mm-shaft version is normally appropriate.

For a metal control-plate installation, the 15mm-shaft version is normally appropriate.

Also confirm that the selected potentiometer body size will fit comfortably in the cavity.

Full-size 24mm controls are normally a good choice for G&L bodies designed around them.

Mini 16mm controls provide additional clearance in smaller or custom cavities.

Do not force a full-size potentiometer into a cavity where it contacts the wall, shielding, switch, jack, PCB, or another control.

Test-Fit the Harness

Before tightening any component permanently, test-fit the complete harness.

Make sure:

all three potentiometers fit their mounting holes
the Pickup Mode switch fits its opening
the output jack has adequate clearance
the central PCB fits comfortably in the cavity
the switch PCB does not contact surrounding hardware
screw terminals remain accessible
the wiring is not pulled tight
and the cavity cover or control plate does not press against a PCB

Leave enough slack for the controls or control plate to be lifted for future service.

Do not shorten wires until you are satisfied with the layout.

Installing the Potentiometers

The GLL1K includes prewired Volume, Treble, and Bass potentiometers.

Install the controls in their respective mounting positions.

The normal control order is:

Volume

Treble

Bass

Do not fully tighten the mounting nuts until the harness has been positioned and all wiring has been checked.

Avoid rotating the potentiometer bodies after the wires have been routed, as this can place unnecessary stress on the connections.

Mini Potentiometer

18mm Shaft

Full Sized Potentiometer

15mm Shaft

Through-Body Installation

This section applies to GLL1K kits using 18mm shafts with 9.5mm threaded bushings.

These versions are intended primarily for rear-routed instruments where the potentiometer shafts pass through the wood of the bass body.

The thicker mounting surface requires the longer shaft and threaded section.

Before tightening the controls, make sure enough shaft extends above the body for the supplied knobs to install correctly.

The potentiometer bodies are separated by wood and therefore are not automatically electrically connected together.

For this reason, every through-body kit includes a dedicated potentiometer grounding strap.

Installing the Through-Body Grounding Strap

The supplied grounding strap has ring terminals for the three potentiometers and a final ground lead.

Install one ring terminal beneath the mounting hardware of each control:

Volume

Treble

Bass

The ring terminals should make direct electrical contact with the metal potentiometer bushings or mounting hardware.

Do not isolate the ring terminal from the metal hardware with a nonconductive washer.

Connect the remaining ground lead to the harness common ground.

After installation, use a multimeter in continuity mode to verify continuity between:

Volume potentiometer body
Treble potentiometer body
Bass potentiometer body
output jack Sleeve
bridge
and harness ground

Control-Plate Installation

This section applies to GLL1K kits using 15mm shafts with 6.5mm threaded bushings.

These versions are intended primarily for instruments using a metal control plate, including many G&L CLF Research models.

Install the potentiometers through the control plate and confirm that the supplied knobs seat properly without bottoming against the plate.

A conductive metal control plate normally bonds the potentiometer bodies together mechanically and electrically.

However, do not assume that mechanical contact guarantees a reliable ground.

Paint, oxidation, coatings, washers, or other hardware can interfere with continuity.

After installation, use a multimeter to verify continuity between:

Volume potentiometer body
Treble potentiometer body
Bass potentiometer body
metal control plate
output jack Sleeve
bridge
and harness ground

The control-plate versions do not require the separate ring-terminal grounding strap supplied with the through-body kits.

Full-Size Potentiometer Installation

The full-size GLL1K versions use potentiometers with approximately 24mm-wide bodies.

These are generally recommended for genuine G&L bodies that were designed with sufficient space for full-size controls.

Before tightening them, confirm that:

the bodies do not touch one another
the switch PCB has adequate clearance
the central PCB has adequate clearance
the output jack does not contact a potentiometer
and the cavity cover or control plate does not press against the controls

Mini Potentiometer Installation

The mini GLL1K versions use approximately 16mm-wide potentiometer bodies.

These provide additional clearance and are generally recommended when installing the harness in a non-G&L body or an unusually compact cavity.

The electrical values are the same as the full-size controls.

There is no intended tonal difference between the mini and full-size versions.

Potentiometer Terminology

When referring to potentiometer terminals:

CCW (lug 1) — counterclockwise lug
Wiper (lug 2) — center lug
CW (lug 3) — clockwise lug

The central GLL1K PCB identifies the relevant potentiometer connections by control and lug number.
For example:
V1 / V2 / V3 — Volume
T1 / T2 / T3 — Treble
B2 / B3 — Bass
Because the controls are supplied prewired, these connections should not normally need to be changed.

The Central Wiring PCB

The central PCB is the electrical hub of the GLL1K harness.

It provides connection points for:

Volume
Treble
Bass
Pickup Mode switch
output
ground

It also carries the passive tone-network components that would otherwise need to be soldered directly between the potentiometer terminals.

This greatly reduces the amount of point-to-point wiring required inside the instrument.

Position the PCB so that the screw terminals remain accessible and the underside cannot contact conductive shielding or other grounded hardware.

Use the supplied self-adhesive neoprene pad where needed to protect the PCB from accidental shorts.

Using the Screw Terminals

Before inserting a wire, loosen the terminal screw enough to open the internal box clamp.

Insert the stripped conductor fully into the terminal.

Make sure no loose strands remain exposed where they could touch an adjacent connection.

Tighten the terminal until the conductor is securely held.

After tightening each terminal, gently pull on the wire to verify that it is actually secured.

It is possible to accidentally insert a wire underneath the internal box clamp instead of inside it. In that situation, the screw may feel tight even though the conductor itself is not securely held.

If a wire pulls free:

loosen the terminal
reposition the conductor inside the clamp
tighten the screw again
perform another gentle pull test

Do not overtighten the terminal screws.

Pickup Wiring

The GLL1K is designed primarily for the standard four-conductor G&L MFD humbucker used in the L•1000.

The Pickup Mode switch PCB handles the coil interconnections required for Parallel, Single Coil, and OMG operation.

For G&L MFD pickups tested by Boscoe Music:

Green and Yellow are associated with the neck-side coil
Black and White are associated with the bridge-side coil
a Blue wire, when present, is used for pickup shielding or baseplate ground

Do not reconnect an unknown pickup solely by color if you are uncertain of its wiring.

For additional pickup identification information, see the Pickup Wiring Reference.

Connecting the Pickup Mode Switch PCB

The three-position ON-ON-ON toggle switch is supplied with a dedicated PCB mounted directly to it.

This PCB performs the coil switching required by the L•1000 without requiring multiple jumpers and passive components to be wired directly to the switch terminals.

Connect the pickup wires to the labeled screw terminals on the switch PCB.

Make sure each conductor is fully captured inside its screw-terminal box clamp.

Do not attempt to duplicate the original point-to-point switch wiring on unused switch terminals.

The PCB already implements the required switching internally.

Pickup Mode Switch

The GLL1K provides the three classic L•1000 pickup modes:

Parallel

Both pickup coils operate in parallel.

This produces the lowest pickup impedance of the three modes and generally provides the clearest, most open response.

Single Coil

Only one MFD pickup coil is active.

This produces a leaner and more focused sound than either two-coil mode.

Because only one coil is operating, Single Coil mode is not hum-cancelling.

Some additional hum or electromagnetic noise compared with Parallel or OMG mode is therefore normal.

OMG

Both pickup coils operate in series at low frequencies.

The OMG capacitor modifies one coil's upper-frequency contribution, creating the characteristic high-output L•1000 OMG response.

The result is a strong low-frequency response with more upper-frequency definition than a conventional full-bandwidth series connection.

OMG mode can be noticeably louder and fuller than Parallel or Single Coil mode.

This is normal.

Understanding OMG Mode

OMG mode does not contain an active bass boost.

The GLL1K is completely passive.

Instead, the pickup coils and capacitor form a frequency-dependent network that allows both coils to contribute strongly at low frequencies while changing the way one coil contributes at higher frequencies.

This produces the characteristic combination of:

strong low end
high output
reduced muddiness compared with ordinary series wiring
and a distinct upper-frequency character

The difference in output between switch positions is therefore expected and is part of the L•1000 design.

Volume Control

The Volume control is a conventional passive 250kΩ audio-taper control.

Turning it clockwise increases output.

Turning it counterclockwise reduces output.

Treble Control

The Treble control is a passive high-frequency cut.

Fully clockwise provides the greatest amount of treble.

Turning the control counterclockwise progressively removes high-frequency content.

The GLL1K includes the 6.8kΩ resistor used in the circuit version selected by Boscoe Music. This resistor is frequently present in CLF Research and Fullerton Deluxe models and serves to set a functional floor for the treble cut.

The Treble control operates in all three pickup modes.

Bass Control

The Bass control is a passive low-frequency cut.

Fully clockwise provides the greatest amount of low-frequency content.

Turning the control counterclockwise progressively reduces low-frequency response.

Because this is a passive circuit, the control does not add bass above the pickup's natural output.

The Bass control may also produce some change in perceived overall level as low-frequency energy is removed.

This is normal.

Output Jack

The GLL1K includes a prewired mono output jack.

The jack connections are:

Tip — audio signal

Sleeve — circuit ground

Because the GLL1K is completely passive, there is no Ring battery-switch connection.

Make sure the jack contacts cannot touch shielding, the control plate, or other grounded hardware.

Bridge Ground

The bridge should be connected to the instrument's common ground.

Preserve the original bridge-ground wire when replacing an existing harness.

Connect it to the appropriate harness ground point.

A missing bridge ground can cause hum that changes when the strings or bridge are touched.

If excessive hum is present after installation, verify continuity between the bridge and output jack Sleeve.

Shielding

Many G&L basses use conductive shielding inside the control cavity.

Copper foil or conductive paint can help reduce electrical noise, but it must be connected to circuit ground to be effective.

If the cavity is shielded:

preserve the original shielding ground
verify continuity between the shielding and circuit ground
make sure the central PCB cannot short against the shielding
make sure the switch PCB cannot contact grounded metal

Use the supplied neoprene pad or other suitable nonconductive insulation where necessary.

Original L•1000 Circuit Variations

G&L used more than one L•1000 wiring arrangement over the model's history.

The GLL1K is based on the circuit version selected by Boscoe Music after comparing original documentation and factory-style wiring.

One notable feature is the 6.8kΩ resistor associated with the Treble circuit. This resistor serves to set a floor to the amount of treble that can be cut.

The GLL1K includes this resistor as part of its central PCB implementation.

The GLL1K also retains the traditional capacitor-based OMG configuration rather than substituting a conventional full-bandwidth series mode.

The intended pickup-mode sequence is therefore:

Parallel

Single Coil

OMG

Before Final Assembly

Before closing the cavity or reinstalling the control plate, inspect the entire harness.

Verify:

You installed the correct 15mm or 18mm shaft version for the instrument.
The potentiometer bodies fit comfortably in the cavity.
All pickup wires are connected to the correct pickup-mode switch terminals.
The pickup shield or baseplate ground, if present, is connected to ground.
The Pickup Mode switch is securely mounted.
All central PCB screw-terminal wires are securely clamped.
Every wire passes a gentle pull test.
No loose conductor strands can touch adjacent terminals.
The Volume potentiometer is correctly connected.
The Treble potentiometer is correctly connected.
The Bass potentiometer is correctly connected.
The output jack Tip carries the signal connection.
The output jack Sleeve is connected to ground.
The bridge ground is connected.
Through-body installations have the grounding strap installed on all three potentiometers.
Control-plate installations have verified continuity through the metal control plate.
The potentiometer bodies have continuity to circuit ground.
Conductive shielding is grounded.
Neither PCB can contact conductive shielding or other grounded metal.
The neoprene pad is installed where needed.
No wires will be pinched when the control plate or cavity cover is installed.

Installing the Knobs

All GLL1K versions use 6mm knurled potentiometer shafts and include matching push-on knobs.

After the potentiometers have been mounted and tested, align each knob carefully with its shaft and press it down using gentle, even pressure.

Do not force the knob farther onto the shaft once it is fully seated.

When removing a knob, lift it evenly from both sides rather than applying excessive force to one side of the shaft.

Testing the Harness

Test the bass before closing the cavity.

Connect the bass to a clean amplifier at a moderate volume.

Start with:

Volume fully up
Treble fully up
Bass fully up

Then test each Pickup Mode switch position.

Parallel

Verify that the sound is clear and full and that both pickup coils are operating.

Single Coil

Verify that the sound becomes leaner and more focused.

Some additional hum is normal because this mode is not hum-cancelling.

OMG

Verify that output and low-frequency response increase substantially.

The sound should be large and powerful while retaining useful upper-frequency definition.

Next test:

the full range of Volume
the full range of Treble
the full range of Bass

Gently move the wiring while the bass is producing sound and listen for intermittent connections.

Only after all controls operate correctly should the cavity be closed.

Complete Wiring Diagram

The diagram below shows the complete GLL1K installation and the relationship between:

MFD pickup
Pickup Mode switch PCB
central wiring PCB
Volume
Treble
Bass
output jack
bridge ground
potentiometer grounding

Troubleshooting

No Output in Any Switch Position

Check the output path first.

Verify:

output jack Tip
output jack Sleeve
Volume connections
central PCB connections
Pickup Mode switch output
and pickup wiring

Perform a gentle pull test on every screw-terminal wire.

A wire inserted underneath the internal box clamp can appear correctly installed without actually making electrical contact.

Output Works in Some Switch Positions but Not Others

If one or two Pickup Mode positions work normally, the output jack, Volume control, and much of the downstream wiring are already known to be functioning.

Inspect:

pickup wires at the switch PCB
switch PCB screw terminals
ON-ON-ON switch
and the affected pickup coil connections

Single Coil Works but Has More Hum

This is normal.

Single Coil mode uses only one coil of the MFD pickup and is therefore not hum-cancelling.

Parallel and OMG modes use both coils and should normally reject more electromagnetic interference.

OMG Is Much Louder Than Parallel

This is normal.

OMG uses both pickup coils in a frequency-dependent series arrangement and can produce considerably greater output and low-frequency energy than Parallel mode.

The difference is part of the intended L•1000 circuit.

OMG Sounds Extremely Bassy

OMG is intentionally the fullest and strongest pickup mode.

First verify that the Bass control is operating normally.

Try reducing the Bass control slightly.

Also confirm that the switch PCB has not been modified and that all pickup conductors are connected correctly.

Bass Control Seems to Change Overall Volume

Some change in perceived output is normal.

The Bass control is a passive frequency-selective network rather than an active equalizer.

Cutting low frequencies also removes energy from the total signal, which can make the instrument seem somewhat quieter.

Treble Control Does Not Behave Normally

The Treble control should progressively reduce high-frequency content as it is turned down.

If it behaves more like an abrupt volume loss rather than a gradual treble cut, inspect its screw-terminal connections and verify that the correct potentiometer is connected to the Treble terminals.

Volume Control Does Not Behave Normally

Verify the Volume potentiometer wiring at:

Because the harness is supplied prewired, inspect the central PCB connections before changing anything at the potentiometer itself.

Excessive Hum in All Modes

Verify:

bridge ground
output jack Sleeve
potentiometer-body grounding
cavity shielding
pickup shield or baseplate ground, if present

For a through-body kit, verify the supplied grounding strap is installed correctly.

For a control-plate kit, verify continuity through the metal control plate.

Use a multimeter to confirm continuity between all grounded components.

If the hum changes significantly when you touch the bridge or strings, inspect the bridge ground.

Works Before the Control Plate or Cavity Cover Is Installed but Fails After Assembly

This usually indicates a short or pinched wire.

Inspect for contact between a PCB and:

conductive shielding
metal control plate
potentiometer body
switch body
output jack
or another grounded component

Also check for wires pinched under the control plate or cavity cover.

Use the supplied neoprene pad where necessary.

Crackling or Intermittent Output

Gently pull each screw-terminal wire.

Make sure every conductor is actually inside the internal box clamp.

Also inspect:

loose strands
wires under mechanical tension
dirty output-jack contacts
loose potentiometer hardware
loose switch hardware

Pickup Wire Colors Do Not Match

Do not guess.

Older G&L pickups or replacement pickups may use different wire colors.

Use a multimeter to identify the individual coils and refer to the Pickup Wiring Reference.

For additional assistance, contact Boscoe Music before modifying the switch PCB or harness.

Final Installation

After the complete harness has been tested:

confirm every screw-terminal connection is secure
verify all grounding connections
confirm the correct grounding method for the selected kit version
position both PCBs away from conductive surfaces
install the neoprene pad where needed
arrange wiring so that it is not pinched or stretched
tighten potentiometer and switch hardware securely but not excessively
install the supplied knobs
reinstall the control plate or cavity cover carefully

Test all three pickup modes and all three controls once more after final assembly.

Need More Help?

For pickup coil identification and G&L MFD pickup wiring information, see the Pickup Wiring Reference.

If you have any questions about installation, compatibility, or troubleshooting, please contact us!

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