Fuse & Relay Panel

The Bentley Service Manual has numerous errors in its list for relays and fuses. Most of those errors have been corrected here! However, it's wise to verify your relays using the relay part numbers listed below, especially for the 1980-1982 cars.

The fuse/relay panel is located under the dash, driver's side, behind the kneebar.  

• 1980-1982 fuse/relay panel part number: 171941821C
• 1983-1993 fuse/relay panel part number: 171941821D

IMPORTANT NOTES:

• Fuse amperage: Green = 30; Yellow = 20; Blue = 15; Red = 10.

• 1980-1982 Cabriolets use ceramic fuses; their amperage is listed on the diagram.  

• 1980-1982 fuel pump relay: Originally installed in position L; due to a recall, the relay should have been moved to position 1 with a wiring loom bridge to position L.
• If your car has factory-installed heated seats, the relays for this option are under each front seat.
• If your car has a factory-installed 2-stage after-run cooling fan system ('88+), the relay for this fan is mounted to the left front fender.
• If your car has factory-installed power windows, there is a control unit beneath the dash on the passenger side.
• If your car has a factory-installed power top, there is a covered thermo-fuse above the relay panel.
• If your car has factory- or dealer-installed daytime running lights, there is most likely a relay attached to the top of the panel (not shown in the diagrams).
• ALL 1983-1993 Cabriolets are CE1

Relay Part Numbers

Relay part numbers, both original and replacement (including aftermarket where available), are now in a PDF, which also contains relay pin diagrams.

Click here for the relay part number guide.

Ground Locations

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Wires

Warm wires

Warm-to-the-touch wires are not at all unusual in these cars, due, in part, to the way they were wired at the factory.

However, wires that become so warm or hot that they melt their insulation and/or smoke are cause for concern.  An overly warm wire is indicative of a circuit with high resistance.  This high resistance can be caused by various issues: bad ground connections, poor wire connections, faulty switch, faulty relay, etc.

Wiring Diagrams

Wiring diagrams can be found in the Bentley Service Manual as well as the Haynes Repair Manual.  NOTE: Those with 1986 Cabriolets should follow both the 1986 and the 1987 Bentley main wiring diagrams; much, but not all, of the wiring in a 1986 resembles the 1987 diagrams and the latter diagrams are easier to read.

Voltage Drop

Voltage drop is a common malady on Cabriolets due to a poorly designed electrical system. Voltage drop can be witnessed on the VDO volt gauge with the engine running: When turning on the headlights, for instance, the volts will drop from 14 down to 12 (the drop is actually more severe when reading the voltage at the battery, then at the headlight; this is because the volt gauge is not 100% accurate); the volt gauge needle will also bounce in rhythm with the turn indicators. If the charging system is in good working order and all ground wires/connections are in good shape, this is nothing to really worry about.  However, to combat voltage drop (and to increase headlight output), install headlight relays, clean all ground contacts and replace ground cables.

Voltage readings (using a DVOM at the battery, not the in-car VDO gauge):

Key-off battery voltage should be 12.6V with a surface charge; 12.3V without a surface charge.

Charging voltage should be 12.8V - 14.7V.

Connecting the OBD Diagnostic Tool

Under the shift boot, towards the front.

NOTE: Only Cabriolets equipped with Digifant I engines have the OBD I diagnostic port; furthermore, an OBD II diagnostic tool cannot be used to pull fault codes from an OBD I system unless it has an adapter!  

Power Windows

Power Windows Don't Work (under construction)

Step 1

Check fuse #17, and the fuse in relay position 17.  Fuses okay? Yes: Proceed to step 2.  No: Replace blown fuse(s).

Step 2

Check for voltage at the power window control unit (located beneath the dash, passenger side; key to battery-on position).  Is there voltage?  Yes: Proceed to step 3.  No: Remove the control unit and check for broken wires, broken internal connections, melted wires/connectors, water.  If there is water intrusion: A) dry the control unit thoroughly; B) reseal the air plenum in the rain tray.  If the control unit is still unresponsive or has melted wires, you'll need to buy a new/used one (part #191959875); and make sure the fuses are good and of proper amperage.

Step 3

Check for voltage at each window switch.  Is there voltage?  Yes:  No:

Step 4

Please refer to this thread and/or this thread and/or this thread on VWvortex for additional info.

Lights

Reverse Lights Do Not Work

If the fuse/relay and bulbs are okay, replace the reverse (back-up) light switch located on top of the transmission (on automatics, the switch is connected to/near the shift lever).

To test the reverse light switch: Disconnect the electrical plug, jump the black and black/blue wire terminals, turn the ignition switch to the battery-on position. If the lights turn on, the switch is faulty.

Headlight Types

Click here to download headlight types document

Headlight Relays  

Whether you are upgrading your headlights or not, it is a very wise idea to relay the headlights.  The stock headlight wiring uses paltry 16 gauge wires, uses the headlight switch as a power source, and contains lengthy wire runs, all of which cause resistance and, ultimately, voltage drop at the headlights thereby reducing each lamp's luminosity.  Adding relays powers the headlights directly from the battery/alternator, will reduce voltage drop in the electrical system, will extend the life of the alternator, headlight switch and ignition switch, will increase the light output giving you whiter & brighter light, and will reduce the chances of the headlight switch overheating.

DIY headlight relay guide

Concept1 headlight relay harness

4Crawler headlight relay harness

LMC Truck headlight relay harness (part #47-3660 36-3580; requires splicing if you have the dual-round grille)

A standard Halogen sealed-beam headlamp produces 100% of its light output at 12.8 volts (or 13.2 volts in Europe) or above.  Take a voltage reading at one of your headlights.  What does your meter read?  My meter read 10.86 volts at each lamp, lo-beam.  Using voltage drop figures found on the Web, at 10.86 volts, each of those headlamps was producing less than 53% of their possible light output.  After adding relays to the headlight circuit, each headlight's voltage jumped up to 13.36 volts, which means the lamps are now producing 100% of their possible light output.

Further information regarding headlight wiring, voltage drop, adding relays, etc. can be found at Daniel Stern Lighting.

Headlight Switches

Three different headlight switch types were used in 1981+ Cabriolets.  If you're replacing the switch, use the information below to ensure you're buying the correct one!  For example, AutohausAZ lists the 321-K switch for a 1990 Cabriolet, which is the wrong one!  (Click on the linked part numbers to see examples.)

Part #321941531G

• 1981 through 1986
• Same switch as below, but with old light symbol (i.e. the two switches are interchangeable)

Part #321941531K

• 1987 to mid-1989 (up to VIN K-009000)
• Same switch as above, but with modern light symbol (i.e. the two switches are interchangeable)

Part #323941531G

• Mid-1989 through 1993 (from VIN K-009001)

Part #323941531H

• Canadian Cabriolets with Daytime Running Lights (from VIN K-011306)
• Headlight switch terminal translations (thanks to Andrew K.):
• TFL = Daytime Running Lights (DRLs)
• NSL = Rear Fog Lamp
• SRA = Headlight Cleaning System

City Lights

If you are installing city lights on a North American Cabriolet, wire the lights to the stock wiring based on how you want the lights to be used.

Stock wiring in the car:

Black = turn signal

Gray = parking/running light

Brown = ground

If you're installing Euro bumper lights that include city lights, you'll need to splice the two ground wires together prior to wiring them to the car's brown ground wires.  

Disabling Day-time Running Lights

Canadian Cabriolets built from 1990-1993 have day-time running lights (DRLs) from the factory, as Canadian law requires DRLs.  If, for whatever reason, you want/need to disable the factory DRL system:Pull the headlight switch and place electrical tape over the TFL pin; reinstall switch.  If your switch does not have a wire going to the TFL pin, or is without a TFL pin: Your car may have hard-wired day-time running lights (DRLs) from the factory.  To disable DRLs on these cars (thanks to Rob for the info): Locate the yellow 20-gauge wire on the back of the headlight switch; either push/pull it out of the harness connector, or cut it and cap/tape it off.  You can also disconnect the same yellow 20-gauge wire from the A-21 pin on the back of the relay panel.

Installing LEDs

Want to brighten up your lights, or change their color, or reduce the power drain?  Replace the original incandescent bulbs with LEDs.  LEDs have come a long way in the last several years.  Rather than buying LEDs and the appropriate resistors, you can now buy LEDs that include resistors for a plug-and-play application in most instances. Download the DIY Guide for a how-to.  Click here for a breakdown of what you need.

Engine Sensors, Senders & Switches

Windshield Wipers

Adding variable wiper option

Look for relay #357955531 or #3B0955531 (has a printed 99. on it in OEM form) found in the following vehicles:

1995-1997 Cabrio & Eurovan

1992-1994 Corrado SLC

1993-1996 Golf/Jetta 2.0L

1990-1997 Passat

Or, order a new one from an auto parts store.  It is a plug and play swap; replace your existing relay with the new one.

To program the variable feature: "Pull the lever into the intermittent position, and, as the wiper does it's sweep, click back into the stop position, if you want a 3 second gap, then wait 3 seconds, and click back into the intermittent position. Bam, you just programmed a 3 second timing."

If ^that doesn't work: "Pull the stalk towards you to (for windshield washers) while the wipers are set to intermittent. This initiates the timer. If left alone at this point it will default to the 20s interval. Pull the stalk towards you again and it will set the timer to that interval, anywhere from 5 to 20 seconds."

Horns

Where are the horns?

The dual-tone horns are mounted to a bracket, which is mounted to the front left frame rail.  Click here for a photo.

Rev Limiters

The K-Jetronic Cabriolets have a rev limiter built into the fuel pump relay.  When the rpm reaches the built-in limit, the fuel pump relay shuts off the fuel pumps.  This is a safety feature; however, the relay can be replaced with a "no-rev" or "hi-rev" version so that the cut-off point is eliminated or increased to approximately 7500 rpm.  Digifant Cabriolets have a rev limiter built into the ECU and cannot be altered.

Fuel Pump Relay Part Numbers and Replacement Equivalents (K-Jetronic only) - see fuel system page for additional info

NOTE: A large batch of KAE relays were made with the wrong circuitry; if you have purchased these relays and the car is still having fuel issues, open the relay to check its circuitry).  Click here for a visual.

Panel Diagrams

1980 - 1982

K-Jetronic

1983 - 1984

K-Jetronic

1985 - 1987

K-Jetronic

July 1987 - 1989*

K-Jetronic

1990 - 1993

Digifant

Diagram

Actual Panel

Diagram

Actual Panel

Diagram

Actual Panel

Diagram

Actual Panel

Diagram

Actual Panel

Click here for a manual supplement containing relay & fuse diagrams, relay panel pin-out schematics, and a guide to reading current flow wiring diagrams.

* Up to 1993 outside North America.

1980 - 1986

1987 - 1989

1990 - 1993

Main ground cables/straps:

• Battery to the left frame rail; frame rail to the transmission
• Valve cover to the ignition coil bracket
• Fender to hood
• A/C compressor to battery (or engine block)
• Ignition Control Unit to battery

Ground locations:

• Fuse/relay panel
• Steering column
• Cold-start valve (K-Jetronic only)
• Trunk, rear left and right
• Dash wiring harness
• Ignition distributor

Main ground cables/straps:

• Battery to the left frame rail; frame rail to the transmission
• Valve cover to the ignition coil bracket
• Fender to hood
• A/C compressor to engine block (or alternator)
• Ignition Control Unit to battery

Ground locations:

• Fuse/relay panel
• Steering column
• Cold-start valve (K-Jetronic only)
• Trunk, rear left and right
• Dash wiring harness
• Engine bay, front left and right ('88+)

Main ground cables/straps:

• Battery to the left frame rail; frame rail to the transmission
• Valve cover to the ignition coil bracket
• Fender to hood
• Digifant ECU to firewall
• A/C compressor to engine block (or alternator)

Ground locations:

• Fuse/relay panel
• Instrument cluster wiring harness
• Steering column
• Trunk, rear left and right
• Engine bay, front left and right
• Horns ('91+)

Please use the Bentley Service Manual wiring diagrams for complete wire routing for your particular car.

Keep your electrical system tip-top by cleaning your electrical connections!

K-Jetronic photos of main grounds.

Digifant photos of main grounds.

Oil System

Part Number

Function

Location

Oil temperature gauge sender

single, white nail-head connector

049-919-563A

Sends oil temp to gauge

Top of oil filter flange

Oil pressure switch & gauge sender

0.3 bar

035-919-561-

Warns, with a flashing light, when oil pressure falls to near zero and sends pressure reading to center console bar gauge

Left side of cylinder head*

Oil pressure switch

1.8 bar ~ 1 pin, white

056-919-081E

Warns, with flashing light and buzzer, when oil pressure falls too low at higher (2000+) rpm

Top of oil filter flange*

Cooling System

Part Number

Function

Location

Coolant temp gauge sender (K-Jetronic)

single, black nail-head connector

049-919-501

Sends coolant temperature to dash gauge and warning system

Top of upper radiator hose flange on cylinder head (1.8L)

Coolant temp gauge sender (Digifant)

black connector

251-919-501D

Sends coolant temperature to dash gauge and warning system

Coolant flange on cylinder head

Coolant temp sensor (Digifant)

blue connector

025-906-041A

Provides an engine temp input to the Digifant control unit that is used to boost fuel delivery to improve cold-running driveability

Coolant flange on cylinder head

Coolant level sensor (Digifant)

251-919-372A

Senses level in coolant expansion tank; when the level is too low, the sensor sends a signal to the warning light in the instrument cluster

In coolant expansion tank

Cooling fan thermo switch

95-84°C, 2-pin, single-speed fan

95-84°C/102-91°C, 3-pin, 2-speed fan

191-959-481B (2-pin)

321-959-481E (2-pin)

191-959-481C (3-pin)

Switches the cooling fan on/off

Lower, left corner of radiator

Oxygen sensor thermo switch (K-Jetronic lambda)

1980-1983

056-919-369AA (25°C)

Bypasses O2 sensor input during cold running for open loop fuel enrichment based on coolant temperature

Note: Original switch is not replaceable; original assembly is NLA. Click on image link at right for replacement details.

Left side of cylinder head in one of the heater hoses

OXS/Lambda probe thermo switch (K-Jetronic lambda)

1984+

035-919-369D (25°C)

027-919-369B (45°C)

Bypasses O2 sensor input during cold running for open loop fuel enrichment based on coolant temperature

(25°C  is standard; 45°C is for cold climates)

Underside of upper radiator hose flange on cylinder head

Thermostat

056-121-113D (87°C)

Controls coolant flow

Inside the lower radiator hose flange on the water pump housing

Thermo-time switch (K-Jetronic)

brown two-pin connector

043-906-163A

Controls operation of cold-start valve when engine is cold based on coolant temperature

Top of upper radiator hose flange on cylinder head

Electrical System

Part Number

Function

Location

Reverse light switch & up-shift indicator

manual transmission

171-919-823A (4-speed)

171-919-823 (5-speed, 1.7L)

191-919-823 (5-speed, 1.8L)

Turns back-up lights on when transmission is put into reverse; disables up-shift system, if installed, when in 5th or reverse gears (see guide for specifics)

On top of transmission bell housing

Reverse light switch

manual transmission  - 1980 (USA), 1988+

020-945-415A

Turns back-up lights on when transmission is put into reverse (see guide for specifics)

On top of transmission bell housing

Reverse light switch

manual transmission  - 4-speed (Europe)

084-941-521 (1.1L, 1.3L)

085-941-521 (1.5L, 1.6L, 1.8L)

Turns back-up lights on when transmission is put into reverse (see guide for specifics)

On top of transmission bell housing

Reverse light switch (aka park-neutral safety switch)

automatic transmission

311-927-147B (to late '90)

155-927-147 (from late '90)

Turns back-up lights on when transmission is put into reverse; prevents car from starting unless gearshift is in Park or Neutral

Base of shift lever in passenger compartment

Brake light switch

up to chassis E-22076

113-945-515H  (2-pin)

113-945-515G  (3-pin)

Turns the brake lights on any time the brake pedal is pressed; works via brake fluid pressure

On/in brake master cylinder

Brake light switch

from chassis E-22077

191-945-515B

Turns the brake lights on any time the brake pedal is pressed; works via electric signal

On brake pedal

Cruise control cut-out switch

manual transmission

811-907-343B

Turns off cruise control system when clutch pedal is pressed; wired into brake light switch

On clutch pedal

Cold-running enrichment vacuum switch (K-Jetronic)

1988-1989

171-919-825B

Interrupts cold-running enrichment above idle

At front of intake manifold off of the vacuum line going to brake master cylinder

Cooling fan after-run thermo switch

1988+

191-919-521B (K-Jet, blue)

191-919-521D (Digi, yellow)

Controls operation of 2-stage cooling fan after-run system based on engine bay temperature (K-Jet: 110°C; Digifant: 100°C). Note: Replacements may not be same color; just be sure that the temp rating is the same.

Back side of cylinder head cover between #3 and #4 cylinders

Idle switch (K-Jetronic)

aka Idle Boost Valve

026-906-283C (no A/C)

026-906-283C (A/C)

Boosts idle speed when rpm's drop to near the stall point; boosts idle speed when A/C compressor engages

Mounted to right strut tower

Idle switch (Digifant)

aka Idle Stabilizer Valve

037-906-457D

Regulates and stabilizes idle speed

Between valve cover and intake manifold

Full-throttle switch

aka enrichment switch, wide open throttle switch

067-133-093 (JH to 1990)

067-906-028 (JH from 1991)

037-133-093D (2H)

Signals control unit with a signal when the throttle valve is fully open for full-throttle enrichment

On throttle body

Mechanical air flow sensor (K-Jetronic)

Measures intake air flow which then operates the control plunger in the fuel distributor for the proper metering of fuel

Under rubber boot on air filter housing, next to the fuel distributor

Electronic air flow sensor (Digifant)

Measures intake air flow; signals from this sensor and the ignition distributor are sent to the ECU for the proper metering of fuel

Side of intake air filter housing

Oxygen sensor

035-906-265B ~ K-Jetronic

034-906-265F ~ K-Jet '88+

030-906-265K ~ Digifant II

030-906-265G ~ Digifant I

Sends signal of combustion efficiency to the ECU for fine-tuning of the air-to-fuel mixture (each fuel injection system processes the signals differently; consult Bentley Manual for further info)

Mounted in exhaust manifold or catalytic converter

Up-shift indicator vacuum switch

manual transmission, 1981-1987

171-919-825B

Relays engine load to the up-shift control unit

Connected to vacuum line to/from distributor

Knock sensor (Digifant)

054-905-377A

Detects harmful detonation in combustion chambers; when it does, ignition timing is retarded in small increments until harmful detonation stops

Front of engine block

* Bentley Service Manual has this gauge's location listed incorrectly.

Table is for reference only; please verify what your car has before ordering parts.