This guide provides detailed instructions on adapting a Vr6 Obd2 engine harness from a MK3 Golf for installation in a Corrado. The goal is to achieve a factory-like fit and functionality. This process requires careful planning and execution, so familiarize yourself with the resources listed below before beginning.
Essential Resources and Tools
Before starting the swap, consult these helpful resources for detailed wiring diagrams and technical information:
- http://the-corrado.net/showthread.php?t=54148
- http://www.corrado-club.ca/forum/viewtopic.php?t=5880
- http://forums.vwvortex.com/showthread.php?3934082
- http://mk2vr6.com/board/viewtopic.php?f=12&t=7831
- http://www.corrado-club.ca/tech/vwecucodes.htm (Verify OBD2 compatibility – Bosch Motronic 3.81)
- http://www.a2resource.com/electrical/CE2.html (Wiring Diagrams)
- http://www.a2resource.com/electrical/management/motronicvr6aba.html (VR6 Engine Management)
- http://www.clubgti.com/showthread.php?219775-Fusebox-FAQ (Fusebox Information)
Essential Tools and Terminals:
- De-pinning Tool: LASER 4328 Terminal Tool Set (or similar) for Junior Power Timer, Micro Timer, and Power Timer connectors.
- Crimping Tool: Uninsulated open barrel F crimp ratchet crimping pliers.
- Terminal Removal Tool
- Heat Shrink Tubing: For labeling de-pinned wires.
- Masking Tape and Pen: Alternative labeling method.
Required Terminals:
- Micro Timer II Socket (female)
- Junior Power Timer Tab (male) – box-shaped wire end.
- Junior Power Timer Socket (female)
- Power Timer Socket (female)
- 6.3mm Female Spade
Key Considerations for VR6 OBD2 Swap
Loom Fitment: The Golf harness requires modifications for proper fitment in the Corrado. Shortening wires at the MAF, carbon canister valve, lambda sensor, rear knock sensor, and fusebox end is necessary.
Auxiliary Coolant Pump: The OBD2 loom’s aux coolant pump wiring needs extending to reach the Corrado’s fusebox. Consider swapping wires from the old loom, extending them, or creating new connections.
MFA Ambient Air Temperature Sensor and AC Switch: Some OBD2 looms lack these components. Retain the corresponding sections from the Corrado’s OBD1 loom or fabricate new ones.
Lambda Power Wire: The OBD2 loom connects the lambda power wire directly to G1/08, often requiring lengthening.
Wiring Harness Comparison and Modification
Carefully compare the Corrado and Golf wiring diagrams before starting. Identify key wires on the OBD2 loom, including:
- Data Line (Grey/White from ECU pin 43)
- Vehicle Speed Sensor (VSS) (Blue/White from ECU pin 65)
- MFA MPG (Violet/White from ECU pin 51)
- Injector Power (Thick Red/Blue wire in yellow plug)
- AC Switch (Green & Blue/Red from ECU pins 37 & 39 – if present)
Step-by-Step VR6 OBD2 Swap Procedure
1. Removing the Old Harness:
Disconnect all connectors at the fusebox, including F, G1, G2, S, Lambda relay, data line, VSS, MFA MPG, AC switch, Z, aux coolant pump, and yellow temp sensor connectors. Retain necessary connectors for the OBD2 loom.
2. Engine Bay Disconnections:
Systematically disconnect components in the engine bay, including the wiper harness, lambda sensor, knock sensors, MAF sensor, carbon canister valve, ambient air temperature sensor (if applicable), ECU plug, engine twist lock connector (T/42), starter, alternator exciter, reverse switch, and crank position sensor.
3. Grommet Considerations:
The Corrado’s bulkhead grommet can be reused if the larger fusebox connectors are de-pinned. The Golf’s wiper loom has different wire colors but the same connections. Address the ECU grommet by using self-amalgamating tape or finding a suitable replacement.
4. Corrado Loom Dimensions:
Reference these measurements to ensure the new loom fits correctly:
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 ] This guide provides a framework for the VR6 OBD2 swap. Always double-check wiring diagrams and exercise caution throughout the process.
