Upgrading Your Corrado Wiring Harness: A Guide to OBD2 PCB Connector Adaptation

Swapping the engine in your VW Corrado can breathe new life into a classic, and often involves integrating a more modern OBD2 engine management system. A crucial part of this upgrade is adapting the wiring harness from an OBD2 vehicle, like a Golf, to fit the Corrado. While existing guides provide a solid foundation for this process, this article focuses specifically on the Obd2 Pcb Connector aspects of this conversion, ensuring a seamless and factory-like integration.

This guide supplements resources like those found on Corrado enthusiast forums, offering detailed insights into modifying an OBD2 Golf wiring harness for your Corrado. It’s based on a manual gearbox ’95 Golf loom, but remember that harnesses from different models or automatic transmissions may vary.

Before starting, it’s essential to identify your ECU type. Bosch Motronic 3.81 ECUs and later are typically OBD2. Useful resources for identifying ECU codes and understanding the electrical systems include:

Essential Tools and PCB Connector Terminals

Adapting the wiring harness professionally means working with the individual terminals within the OBD2 PCB connectors of your fuse box. Ideally, avoid cutting wires by using de-pinning tools designed for Junior Power Timer connectors and other types commonly found in automotive PCBs (Printed Circuit Boards). Testing the OBD2 loom in your car before making any permanent cuts is always a wise precaution.

A reliable terminal tool set, such as the LASER 4328 Terminal Tool Set, is highly recommended. This kit handles Micro Timer, Junior Power Timer, Power Timer, and spade connectors, proving to be more effective than many generic or DIY tools.

You can source replacement terminals for your fuse box PCB connectors from suppliers like Polevolt or RS Online, searching for “junior power timer connectors”. eBay is another viable option for these components. Consider investing in “Uninsulated open barrel F crimp ratchet crimping pliers” for secure terminal crimping.

Key terminals you’ll likely need include:

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 or masking tape to label de-pinned wires. This will prevent confusion when reassembling the PCB connectors.

Loom Fitment and Adapting PCB Connector Wiring Lengths

The OBD2 Golf loom has a slightly different shape compared to the Corrado harness. To achieve a factory-like fit, some wires will need shortening, particularly at the MAF sensor, carbon canister valve, lambda sensor, rear knock sensor, and the fuse box end – all areas involving OBD2 PCB connectors. Having terminal removal and crimping tools, along with Junior Power Timer and Standard Timer connectors, is essential for this process. Skipping this step will result in excess wiring, especially around the ECU area and its associated PCB connectors.

Addressing Specific Wiring Adaptations Related to PCB Connectors

Several circuits require specific attention when adapting the OBD2 loom, often involving modifications at the PCB connector level:

Auxiliary Coolant Pump

In the Corrado, the auxiliary coolant pump circuit runs through pin 31 of the 42-pin Engine Connector (T/42) and then to the fuse box. The OBD2 loom, however, routes it directly from T/42 to the fan control module, making it too short for the Corrado setup. The same applies to the trigger wire from pin 3 of the yellow temperature sensor (pin 9 on T/42).

These two wires need to be extended, replaced, or swapped from the Corrado loom to reach the fuse box PCB connectors. To replace them, 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
Approximately 2.12m each of Brown/Red and Red/black 0.5mm thinwall cable.

Alternatively, consider transferring the fan control module and its wiring from the Golf loom if available, although ensure compatibility with the Corrado’s 3-speed fan system.

MFA Ambient Air Temperature Sensor

Some OBD2 looms might lack wiring for the MFA ambient air temperature sensor. If this is the case, retain this section from your OBD1 loom or create a new circuit. This involves:

1x 2-way Female JPT Housing
4x Junior Power Timer Sockets (2 for fuse box PCB connectors, 2 for JPT housing)
Approximately 2.10m each of Brown/White and White/Red 0.5mm thinwall cable.

Air Conditioning (ON) Switch

Similarly, some OBD2 looms may omit the wiring for the AC (ON) switch. You might need to fabricate this section, requiring:

2x Micro Timer Socket terminals
Approximately 2m each of Green and Blue/Red 1mm thinwall cable.

Lambda Power Wire

The Corrado lambda sensor power runs through a relay (Type 53), whereas OBD2 systems often connect directly from fuse box location G1/08. If the OBD2 loom wire is too short, replace it with:

2x Junior Power Timer Sockets
Approximately 1.7m of Red/White 1mm thinwall cable.

Verifying Both Looms and PCB Connector Compatibility

Before any modifications, thoroughly check both the Corrado and Golf wiring looms. Compare the wiring diagrams, paying close attention to Plugs F, G1, G2, and S, which are crucial for this conversion and heavily involve OBD2 PCB connectors in the fuse box.

[Image of Fuse Box Connectors – original article attachment 78946, 78947, 78948, 78949, 78950, 78937, 78938, 78939, 78940, 78941, 78942, 78943, 78944, 78945 with updated alt text]

Identify these wires on the OBD2 loom:

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

If all necessary wires are present and the loom is undamaged, proceed with the adaptation.

Step 1: Removing the Original Corrado Harness PCB Connectors

Begin at the fuse box. Unplug the following connectors, noting that yellow plugs might not always be connected:

Fuse Box PCB Connectors (Female Junior Power Timer connectors unless stated):

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 – Data Line 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 (unused, near starter)

Retain some of these connectors, as they will be needed for the OBD2 loom integration and its PCB connectors.

[Image of Removed Corrado Harness – original article attachment 78933 with updated alt text]

Step 2: Engine Bay Disconnections

Moving to the engine bay, disconnect:

Wiper harness (at the wiper motor) – remove grommet (save both grommet and wiper motor harness grommet).
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 (keep if the new 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

Step 3: Grommet Considerations for PCB Connector Wire Routing

For a clean installation, grommets are critical where wiring harnesses pass through the bulkhead. If you de-pin the larger fuse box PCB connectors (F, G1, G2, S), you can reuse the Corrado bulkhead grommet, as the Golf grommet is typically too large. If using the Golf wiper loom, note the wire colors may differ, but connections remain the same. Also, keep the small grommet from the wiper motor harness.

The ECU grommet is more challenging. Either build up the OBD2 loom with self-amalgamating tape to fit the Corrado hole, find a 50mm replacement grommet, or carefully cut and glue the old grommet onto the new loom to ensure proper sealing around the PCB connector wires.

The Corrado loom features a grommet on the T/42 connector, which the OBD2 loom may lack. If desired, parts 1H0971840A (grommet) & 1H0973132A (retaining ring) can be added, but this requires removing all terminals from T/42.

Step 4: Corrado Loom Dimensions for Accurate OBD2 PCB Connector Placement

To ensure the adapted OBD2 loom fits like the original Corrado harness, use the following dimensions as a guide. These measurements are crucial for positioning the PCB connectors and components correctly within the engine bay and fuse box area.

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 meticulously following these steps and paying close attention to the OBD2 PCB connectors and wiring modifications, you can successfully adapt an OBD2 Golf wiring harness for your Corrado, ensuring a reliable and integrated engine management system upgrade. Remember to always double-check connections and wiring diagrams throughout the process.