Electrical Connections
The electrical components for the TDI consist of:
The relays and resistors are wired so that the filter heater operates when the engine is starting or running but is cold, and the signal from the engine's standard coolant temperature sensor is modified by placing resistors in series with the signal according to the following rules:
These modifications apparently make the engine computer "think" that the engine is colder than it actually is, so as to supply power to the glow plugs longer than it normally would.
The Mercedes modifications were different, perhaps with fewer relays and different logic.
Kent drills through strut tower to mount a relay
Todd's Golf TDI, with mounting locations for all three relays highlighted.
This view shows the place where the resistors are mounted - inside the stock relay box. Just to the right is the channel which contains three wiring harnesses, one of which must be cut to access the coolant sensor wire. There were two small harnesses and one larger harness. Alexander said the way he tells which one to cut is to feel the two smaller ones and find the one with smaller wires in it.
Here, he has just begun to cut into the harness.
Now he has located the blue wire from the coolant sensor and cut it. After splicing the proper relay wires to these two points, he used electrical tape to re-bind the harness, nice & neat! When you put the cover back on this channel, there are several new wires that mechanically interfere with the cover. We had to cut away part of the cover to make it fit.
There's another electrical connection into the harness that runs just behind the fans. In this one, you have to splice onto the blue wire without cutting it. Unfortunately, all the wires in the harness are double insulated and the outside insulation is black. Alexander noted that you can just see the colors at the ends of the wires a few inches away at a connector, and that's how he tells which one to strip.
Here it is after wiring and re-wrapping with electrical tape.