Electrical System

General Infoexpand_more

Fuse & Relay Panel  expand_more

General Info Diagrams Electrical System Guide

Relays Ground Locations Wiring Voltage Drop OBD I Diagnostics Power Windows

Lights  expand_more

General Info Headlight Types Headlight Relays Headlight Switches City Lights Installing LEDs

Sensors, Senders, Switches Windshield Wipers Horns Rev Limiters

Troubleshootingexpand_more

Warm Wires Voltage Drop Reverse Lights Don't Work OBD I Diagnostics Power Windows Don't Work

DIY Guidesexpand_more

Adding Variable Wiper Option Bulb Cross-reference Installing LEDs Disabling DRLs Adding Headlight Relays Lights-on Warning Relay Fuse 5 Circuit Split Reverse Light Switches Connecting OBD Scan Tool Increasing Alternator Output Refurbing Dash Switches Diagnosing Electrical Issues Installing CE2 MFA Cluster Aiming the Headlights Side-markers to Turn Signals Installing Fog/Auxiliary Lights Installing Mk3 Courtesy Light Fixing Slow Wipers Variable Speed Wiper Mod Wiper Motor Swap DIY Power Window Controller Instrument Cluster Diagrams How To Read Wiring Diagrams

☰

Updated: 31-Mar-2024

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. Fuse & Relay Panel.

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:

• 1983-1993 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
• List of DIN electrical terminal designations

Relays

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

Relay part number guide:

Ground Locations

Wiring

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.

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.

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.

OBD Diagnostics

Test ports are accessed under the shift boot, towards the front.

NOTE: Only Cabriolets equipped with Digifant I fuel injection have the OBD I diagnostic ports. Furthermore, an OBD II diagnostic tool cannot be used to pull fault codes from an OBD I system unless it has an adapter!

OBD I diagnostics guide:

Power Windows

Power Windows Don't Work (under construction)

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


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.


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


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

Lights

Headlight Types

Headlight guide:

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
• 4Crawler headlight relay harness
• LMC Truck headlight relay harness (part #47-3660 choose #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! Tap on the icons 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:

1. Pull the headlight switch and place electrical tape over the TFL pin
2. 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):

1. Locate the yellow 20-gauge wire on the back of the headlight switch
2. Either push/pull it out of the harness connector, or cut it and cap/tape it off
3. 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. Tap here for a breakdown of what you need.

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.

Sensors, Senders, Switches

Oil System	Part Number	Function & Location
Oil temperature gauge sender single, white nail-head connector	049-919-563A	Function: Sends oil temp to console gauge, or MFA instrument cluster Location: Top of oil filter flange
Oil pressure switch & gauge sender 0.3 bar, 2-pin	035-919-561	Function: Warns, with a flashing light, when oil pressure falls to near zero and sends pressure reading to center console bar gauge Location: Left side of cylinder head*
Oil pressure switch & MFA gauge sender 1.8 bar, 2-pin	035-919-561A	Function: Warns, with a flashing light, when oil pressure falls to near zero and sends pressure reading to MFA instrument cluster Location: Oil filter flange
Oil pressure switch 0.3 bar	028-919-081D 056-919-081C	Function: Warns, with a flashing light, when oil pressure falls to near zero Location: Left side of cylinder head
Oil pressure switch 1.8 bar ~ single, white nail-head connector	056-919-081E	Function: Warns, with flashing light and buzzer, when oil pressure falls too low at higher (2000+) rpm Location: Oil filter flange*
Cooling System	Part Number	Function & Location
Coolant temp gauge sender K-Jetronic single, nail-head connector	049-919-501	Function: Sends coolant temperature to dash gauge and warning system Location: Top of upper radiator hose flange on cylinder head (1.8L)
Coolant temp gauge sender Digifant black connector	251-919-501D	Function: Sends coolant temperature to dash gauge and warning system Location: Coolant flange on cylinder head
Coolant temp sensor Digifant blue connector	025-906-041A	Function: Provides an engine temp input to the Digifant control unit that is used to boost fuel delivery to improve cold-running driveability Location: Coolant flange on cylinder head
Coolant level sensor 2H, DX engines	251-919-372A	Function: 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 Location: In coolant expansion tank
Cooling fan thermoswitch 95-84°C 2-pin, single-speed fan	2-pin: 191-959-481B 321-959-481E	Function: Switches the cooling fan on/off Location: Lower, left corner of radiator
Cooling fan thermoswitch 95-84°C/102-91°C 3-pin, two-speed fan	3-pin: 191-959-481C	Function: Switches the cooling fan on/off Location: Lower, left corner of radiator
Oxygen sensor thermoswitch K-Jetronic lambda 1980-1983	25°C: 056-919-369AA	Function: 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. Tap on image icon below for replacement details. Location: Left side of cylinder head in one of the heater hoses
Oxygen sensor thermoswitch K-Jetronic lambda 1984+	25°C: 035-919-369D (standard) 45°C: 027-919-369B (cold climates)	Function: Bypasses O2 sensor input during cold running for open loop fuel enrichment based on coolant temperature. Location: Underside of upper radiator hose flange on cylinder head
Thermostat	87°C: 056-121-113D	Function: Controls coolant flow Location: Inside the lower radiator hose flange on the water pump housing
Thermo-time switch K-Jetronic lambda brown two-pin connector	043-906-163A	Function: Controls operation of cold-start valve when engine is cold based on coolant temperature Location: Top of upper radiator hose flange on cylinder head
Electrical System	Part Number	Function & Location
Reverse light switch & upshift indicator manual transmission	4-speed : 171-919-823A 5-speed, 1.7L: 171-919-823 5-speed, 1.8L: 191-919-823	Function: 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) Location: On top of transmission
Reverse light switch manual transmission 4-speed 5-speed 1988+	1.1L, 1.3L: 084-941-521 1.5L, 1.6L, 1.8L: 085-941-521	Function: Turns back-up lights on when transmission is put into reverse (see guide for specifics) Location: On top of transmission
Reverse light switch manual transmission 4-speed	020-945-415A	Function: Turns back-up lights on when transmission is put into reverse (see guide for specifics) Location: On top of transmission
Reverse light switch automatic transmission	to late '90: 311-927-147B from late '90 155-927-147	Function: Turns back-up lights on when transmission is put into reverse; prevents car from starting unless gearshift is in Park or Neutral Location: Base of shift lever in passenger compartment
Brake light switch up to chassis E-22076	2-pin: 113-945-515H 3-pin: 113-945-515G	Function: Turns the brake lights on any time the brake pedal is pressed; works via brake fluid pressure Location: On/in brake master cylinder
Brake Light Switch from chassis E-22077 also cruise control cut-off switch in auto trans	191-945-515B	Function: Turns the brake lights on any time the brake pedal is pressed; works via electric signal Location: On brake pedal
Cruise Control Cut-off Switch manual transmission	811-907-343B	Function: Turns off cruise control system when clutch pedal is pressed; wired into brake light switch Location: On clutch pedal
Cold-running Enrichment Switch K-Jetronic 1988+	171-919-825B	Function: Interrupts cold-running enrichment above idle Location: At front of intake manifold off of the vacuum line going to brake master cylinder
Cooling fan after-run thermoswitch 1988+ K-Jet: 110°C Digifant: 100°C	K-Jet, blue: 191-919-521B Digi, yellow: 191-919-521D	Function: Controls operation of 2-stage cooling fan after-run system based on engine bay temperature Note: Replacements may not be same color; just be sure that the temp rating is the same. Location: Back side of cylinder head cover between #3 and #4 cylinders
Idle Boost Valve K-Jetronic	A/C: 026-906-283C No A/C: 026-906-283B or 026-906-283H	Function: Electromagnetic solenoid valve that controls operation of 2-stage cooling fan after-run system based on engine bay temperature Note: Replacements may not be same color; just be sure that the temp rating is the same. Location: Mounted to right strut tower
Idle Stabilizer Valve Digifant	037-906-457D	Function: Regulates and stabilizes engine idle speed Location: Between valve cover and intake manifold
Full-throttle Switch aka: enrichment switch, wide open throttle switch	K-Jetronic: 067-133-093 067-906-028 Digifant: 037-133-093D	Function: Signals control unit with a signal when the throttle valve is fully open for full-throttle enrichment Location: On throttle body
Mechanical Airflow Sensor K-Jetronic	n/a	Function: Measures intake air flow which then operates the control plunger in the fuel distributor for the proper metering of fuel Location: Under rubber boot on air filter housing, next to the fuel distributor
Electronic Airflow Sensor Digifant	n/a	Function: Measures intake air flow; signals from this sensor and the ignition distributor are sent to the ECU for the proper metering of fuel Location: Side of intake air filter housing
Oxygen Sensor K-Jetronic	1-wire: 035-906-265B 3-wire: 034-906-265F	Function: 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) Location: Mounted in exhaust manifold or catalytic converter
Oxygen Sensor Digifant	Digifant II: 030-906-265K Digifant I: 030-906-265G	Function: 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) Location: Mounted in exhaust manifold or catalytic converter
Upshift Indicator Vacuum Switch manual transmission 1981-1987	171-919-825B	Function: Relays engine load to the upshift control unit Location: Connected to vacuum line to/from distributor
Knock Sensor Digifant	054-905-377A	Function: Detects harmful detonation in combustion chambers; when it does, ignition timing is retarded in small increments until harmful detonation stops Location: Front of engine block
* Bentley Service Manual has this switch's location listed incorrectly. Table is for reference only; please verify what your car has before ordering parts.

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, Tap back into the stop position, if you want a 3 second gap, then wait 3 seconds, and Tap 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.

Rev Limiters

K-Jetronic:

Rev limiter is 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.

• Fuel Pump Relay Part Numbers and Replacement Equivalents:
• See the fuel system page for additional important information

Digifant: