Swapping a VR6 engine into a Corrado is a popular and rewarding upgrade. However, integrating an OBD2 wiring harness from a Golf can present challenges. This guide builds upon existing resources to provide a detailed walkthrough for adapting an OBD2 Golf wiring loom to fit your Corrado, maintaining a factory-like finish.
Before you begin, it’s crucial to familiarize yourself with these essential guides:
- Corrado Forum OBD2 Swap Guide
- Corrado Club Canada VR6 Wiring Info
- VW Vortex MK2 VR6 OBD2 Harness Help
- MK2 VR6 Wiring Harness Guide
This article serves as a supplementary resource, specifically focusing on modifying an OBD2 Golf wiring harness for a seamless Corrado installation. We aim to address common sticking points and provide practical solutions based on real-world experience.
This guide utilizes a wiring harness from a manual 1995 Golf. Be aware that OBD2 harnesses can vary depending on the donor vehicle’s model year, transmission type (automatic or manual), and auxiliary features. Always verify compatibility before proceeding.
To identify your ECU type, consult this helpful resource:
Any Bosch Motronic 3.81 ECU is OBD2 compliant.
For essential wiring diagrams and fuse box information, refer to these links:
Essential Tools and Terminals for OBD2 VR6 Harness Adaptation
Adapting the wiring harness without cutting wires is achievable with the right tools. Investing in de-pinning tools for Junior Power Timer connectors is highly recommended. While cutting is an option, testing the OBD2 loom in your car before making any permanent cuts is a prudent step.
A reliable terminal tool set, such as the LASER 4328 Terminal Tool Set, is invaluable. This set includes tools for Micro Timer, Junior Power Timer, Power Timer, and spade connectors, proving to be effective where other generic tools might fail.
For fuse box connections, you can source terminals from suppliers like:
- Polevolt Terminals
- RS Online Junior Power Timer Connectors
- eBay (search for “Junior Power Timer terminals”)
Crimping pliers, specifically “Uninsulated open barrel F crimp ratchet crimping pliers” (available on eBay), might be necessary for secure terminal crimping.
The following terminals are commonly used in this adaptation:
- Micro Timer II Socket (female)
- Junior Power Timer Tab (male) (choose the boxed wire-end type)
- Junior Power Timer Socket (female)
- Power Timer Socket (female)
- 6.3mm Female Spade
Organization is key. Print a list of fuse box terminal locations (G1/01, G1/02, etc.) and use 6mm clear heat shrink tubing or masking tape to label de-pinned wires. This prevents confusion and ensures accurate reconnection.
Loom Fitment Considerations for OBD2 VR6 into Corrado
The Golf and Corrado wiring looms have slightly different shapes. For an optimal, factory-like fit in your Corrado, some wires in the OBD2 loom will need shortening. Key areas for adjustment include the MAF sensor, carbon canister valve, lambda sensor, rear knock sensor, and the fuse box end.
Alt text: Key components of an OBD2 VR6 wiring harness for engine swaps, including MAF sensor, lambda sensor, ECU connectors, and fuse box terminals.
Having terminal removal and crimping tools, along with Junior Power Timer and Standard Timer connectors on hand is essential for these modifications. If you skip wire shortening, expect excess loom, especially around the ECU area.
Addressing Specific Wiring Issues: Auxiliary Coolant Pump, MFA, AC, and Lambda
Auxiliary Coolant Pump:
In the Corrado loom, the auxiliary coolant pump circuit runs through pin 31 of the 42-pin Engine Connector (T/42) and then to the fuse box, connecting to the Fan Control Module. The OBD2 loom routes this directly from pin 31 on T/42 to the Fan Control Module, making it too short for the Corrado.
The same length issue applies to the trigger wire from pin 3 of the yellow temperature sensor (for fans and aux coolant pump after-run), which connects to pin 9 on T/42.
Alt text: Diagram illustrating the difference in wiring loom routing between Corrado and Golf for OBD2 VR6 conversions, highlighting the auxiliary coolant pump circuit.
To resolve this, you can either:
- Swap these two wires from the Corrado loom.
- Extend the existing wires.
- Replace the wires entirely from T/42 to the fuse box.
For wire replacement, you’ll need:
- 2x Micro Timer socket terminals for the T/42 connector
- 1x JPT tab (male) terminal for the Red/Black wire at the fuse box
- 1x 6.3mm Female Spade for the Brown/Red wire at the fuse box
- 2.12m of Brown/Red and 2.12m of Red/black 0.5mm thinwall cable
Alternatively, consider transferring the Fan Control Module and its associated wiring from the Golf loom, if available. However, Golf looms may have a 2-speed fan controller, while Corrados often use a 3-speed version. The fan controller loom typically requires a live feed from A1/05 for the fan thermoswitch, earth wires, and a battery live connection.
MFA Ambient Air Temperature Sensor:
Some OBD2 looms lack wiring for the MFA ambient air temperature sensor. If your new loom is missing this, retain this section from your OBD1 Corrado loom or create a new one.
Components needed for a new MFA sensor circuit:
- 1x 2-way Female JPT Housing
- 4x Junior Power Timer Sockets (2 for fuse box, 2 for JPT housing)
- 2.10m of Brown/White & 2.10m White/Red 0.5mm thinwall cable
Air Conditioning (ON) Switch:
Similar to the MFA sensor, some OBD2 looms may not include wiring for the air conditioning (ON) switch. If absent, reuse the Corrado OBD1 section or fabricate a new circuit.
Parts for a new AC switch circuit:
- 2x Micro Timer Socket terminals
- 2m of Green & 2m Blue/Red 1mm thinwall cable
Lambda Power Wire:
In the Corrado, the lambda sensor power runs through a relay (Type 53). OBD2 systems often route it directly from G1/08 in the fuse box. If the OBD2 loom’s wire is too short, replace it.
Parts for a longer lambda power wire:
- 2x Junior Power Timer Sockets
- 1.7m of Red/White 1mm thinwall cable
Verifying Both Looms: Corrado vs. OBD2 Golf
Before commencing the adaptation, thoroughly compare both the Corrado and Golf wiring looms. Use wiring diagrams (links provided earlier) to create a spreadsheet comparing the main wiring plugs (F, G1, G2, and S for this conversion).
Alt text: Detailed wiring diagram for OBD2 VR6 engine swap into a Corrado, showing ECU pinouts and fuse box connections.
Key wires to identify on the OBD2 loom include:
- Data Line: Grey/White wire from ECU pin 43
- Vehicle Speed Sensor (VSS): Blue/White wire from ECU pin 65
- MFA MPG: Violet/White wire from ECU pin 51
- Injector Power: Thick Red/Blue wire (Yellow Plug)
And if applicable:
- AC (On) Switch: Green & Blue/Red wires from ECU pins 37 & 39
Ensure all essential wires are present and correctly located, and that the loom is free from damage before proceeding with the adaptation.
Step-by-Step Guide: Removing the Old Corrado Harness
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Fuse Box Disconnection: Begin at the fuse box and unplug the following connectors (some yellow plugs may be unconnected):
- F – (White Plug) 10 Pin – Engine Harness Near Gearbox
- G1 – (White Plug) 12 Pin – Engine Harness Engine Sensors
- G2 – (White Plug) 12 Pin – Engine Harness Engine Sensors
- S – (White Plug) 5 Pin – Wiper Motor Harness
- Lambda Relay: 4 Pin Female Spade Connectors
- Data Line (Brown Plug): 2 Pin – Yellow & Grey/White wires
- Vehicle Speed Sensor (VSS) (Blue Plug): 1 Pin – Blue/White wire
- MFA MPG (Black Plug): 1 Pin – Violet/White wire
- AC (on) Switch (Yellow Plug): 2 Pin Male JPT – Green & Blue/Red wires
- Z – (Red Plug) 1 Pin Red/Yellow wire
- Aux Coolant pump (Red Plug): 1 Pin Male JPT – Red/Black wire
- Yellow Temp Pin 3 (White Plug): 1 Pin Female Spade Connector – Brown/Red wire
- (Yellow Plug): 1 Pin – Yellow/Black wire (often unused, terminates near starter)
Alt text: Diagram of the Corrado fuse box highlighting connector locations for OBD2 VR6 wiring harness swap, including plugs F, G1, G2, and S.
Retain some of these connectors, as they may be needed for the OBD2 loom.
Alt text: Collection of Corrado wiring harness connectors detached from the fuse box, prepared for integration with the OBD2 VR6 loom.
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Engine Bay Disconnection: Move to the engine bay and disconnect:
- Wiper harness (at wiper motor) and remove the grommet (save both).
- Lambda 4 Pin Connector
- Rear Knock Sensor 3 Pin Connector
- MAF sensor 4/5 Pin connector
- Carbon canister valve 2 Pin
- Ambient air temp sensor 2 Pin (retain if your OBD2 loom lacks one)
- 68 Pin ECU plug
- 42 Pin Engine Twist Lock connector
- Starter 1 Pin Red/Black
- Front Knock Sensor 3 Pin
- Crank Position Sensor 3 Pin
- Alternator exciter 1 Pin Blue Wire
- Reverse Switch 2 Pin
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Grommet Management:
- Bulkhead Grommet: If you de-pin the larger fuse box connectors (F, G1, G2, S), you can reuse the Corrado bulkhead grommet. The Golf grommet is typically too large. If using the Golf wiper loom, note that wire colors may differ, but connections remain consistent. Keep the small grommet from the wiper motor harness.
- ECU Grommet: The ECU grommet can be tricky. Build up self-amalgamating tape to secure the new loom in the hole, find a 50mm replacement grommet, or carefully cut and glue the old grommet onto the new loom.
- T/42 Connector Grommet: The Corrado loom has a grommet on the T/42 connector, which is absent in many OBD2 looms. If desired, parts are available (1H0971840A for grommet & 1H0973132A for retaining ring), but require terminal removal from T/42 for installation.
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Corrado Loom Dimensions (Reference):
To ensure a similar fit with the new loom, you can measure your old Corrado loom or use the diagram below as a guide for wire lengths between components. This will help in shortening wires on the OBD2 loom for a cleaner installation.
FUSEBOX CONNECTORS |---|---| 0.4m |---|---| BULKHEAD GROMMET |---|---| 0.26m |---|---| |----0.97m----|---0.15m----[ LAMBDA SENSOR ] |---|---| |----0.17m----[ REAR KNOCK SENSOR ] (0m) |---|---|----0.97m----|----0.10m----[ MAF ] |---|---| |----0.25m----[ CARBON CANISTER VALVE ] | 0.60m |---|---| |----0.22m----I ECU GROMMET I----0.17m---[ ECU PLUG ] |---|---| 0.48m |---|---| |----0.47m----[ ENGINE TWIST CONNECTOR ] |---|---| |----0.58m----|----0.14m----[ STARTER ] |---|----0.15m----[ ALTERNATOR EXCITER ] |---|----0.17m----[ FRONT KNOCK SENSOR ] |---|----0.17m----[ REVERSE SWITCH ] |---|----0.18m----[ CRANK POSITION SENSOR ]By following these steps and carefully adapting the OBD2 Golf wiring harness, you can achieve a successful and professional-looking VR6 engine swap in your Corrado. Remember to always double-check wiring diagrams and test connections before final assembly.
