Tdi transplants – wiring up the engine

A common question asked on internet forums and occasionally be email to me is how to wire up a Tdi fitted to a Series vehicle.  In short, it’s simpler than you might think. If starting with a petrol powered vehicle, you have it especially easy.

Petrol:

The battery cable needs to be run directly to the starter solenoid’s ring terminal stud, with the original solenoid near the battery removed.  The alternator wires need to be run to the same stud, as do the thick brown feeds to the dash (fuse box and ignition switch).  The starter solenoid’s control wire (white with a red strip) needs to be run to the new solenoid position on top of the starter motor instead of the old solenoid near the battery.  the coolant temperature sender wire still connects to the sender in the thermostat housing, but you need to fit the Series sender to the Tdi for gauge compatibility.  If the threads don’t match, you may need a late SIII metric sender.  The oil pressure warning light wire (white with brown stripe) connects to the pressure switch on the filter housing as before, and the coil’s low tension wire (white with light blue stripe) is extended to control the fuel solenoid on the injection pump.

The biggest problem is the heater plugs.  You can use a heavy duty switch in the dash or seat base to rig a separate (fused) circuit directly from the battery to the plugs, with the positive side of the dash warning light connected to the no.4 plug, or you can fit the timed relay from a Tdi equipped vehicle, using the photo in this post  as a guide of how to wire it up the way LR did.  This will give you automatic activation of the glow plugs when selecting the I”I” position of the ignition switch (engine run position), with automatic disconnection on timing expiry or on starter motor activation (ensures maximum battery power for the starter motor).

Diesel:

Wiring up the battery, alternator, starter, dash loom, temperature sender and oil pressure warning are exactly as per the petrol model above.  The differences lie in the heater plugs and the fuel control.

The heater plugs are very simple this time – just connect the no.4 heater plug to the vehicle’s existing circuit, bypassing the ballast resistor mounted on the bulkhead (either fit the battery feed and the wire to the plugs to the same terminal on the resistor mounting, or remove the resistor outright and permanently join the old feed and new plug wire.  The dash warning bulb can be connected to the no.4 plug.

The injector pump’s solenoid needs a separate dash switch to control it, and has to be fed from a permanent live in the fuse box or dash – the green “I” and white”II” wires in the vehicle loom are unpowered when cranking the diesel engine (to ensure all power goes to the plugs and starter), so are no good for feeding power to the fuel solenoid.  The new switch should have a fuse (10A will be more than enough) and can be concealed if preferred to make vehicle theft more difficult to the opportunist.