Early ALH TDI 7 Pin Glow Plug Relay & Pinout

I only had the engine harness from my donor car, so it was necessary to wire in the glow plug relay without the OEM socket. Took a while to figure out exactly the function of some of the wires. The wiring diagram was not very clear as to what wire went to the labeled terminals on the relay. I am going to summarize my setup below for my own future reference.

Relay pin 30

• This is the largest terminal on the relay, and is wider than your normal sized spade connector. This is a fused 50a circuit from battery positive. I finally found the wide spade connectors at Northern Tool.

Relay pin G1/2

• Switched power wire to glow plugs 1 & 2. Self explanatory.

Relay pin G1/2 

• Switched power wire to glow plugs 3 & 4. Self explanatory.

Relay pin 31

• Control side ground. I attached this wire to ground via eyelet on the same bolt that I grounded the fuel pump.

Relay pin 86

• Control side positive. This is powered by the ECM relay (yellow wire in my case).

Relay pin ST

• ECM to relay. ECM uses this wire to activate the relay when specified conditions are met where the glow plugs are to be on. 5v signal. White/purple wire. ECM pin T80/42.

Relay pin D1

• 5v signal back to ECM when ST pin is powered. This circuit provides feedback to the ECM that includes fault checking. Green wire. ECM pin T80/37.

With this configuration, the glow plugs worked perfectly the first time I tried it. With the ECT sensor unplugged, my ammeter read 49 amps on relay pin 30 with the key on. After the engine starts, the amp draw went down to 24 to 25 amps. Only glow plug fault remaining is for an open circuit to the GP light, which I have not yet wired.

This wiring information is for the Bosch OEM relay, part #038 911 253. Use the above information at your own risk. The data I posted above is correct for my application, may not be accurate for your application. Double check & triple check your wiring diagrams. Figure out & understand exactly what each wire does. Do your own research. Learn how things work. Write notes so you don't forget. If you screw this up and damage something, it is entirely your fault!