Function of the 3 pin connector near the ECU

[Jean]

I extended my stock wiring harness today and wire by wire figured out (or more like confirmed by cutting the wires in the harness extension) function of each wire in the harness, as I had some questions I wanted confirmed before I wrap up my harness adapter.

This applies only to those with early cars and the rectangular 19 pin C101 engine harness connector.





My extension lol





Started cutting wires by at a time to confirm their function/effect







fuel pump wire










The following wires are needed to start the car.

6 - power fused
7 - fuel pump
8 - power while starting
10 - power no fused

Then the following should be connected as well

1 - D+ alternator (triggers the battery light in the cluster)
4 - controls the coolant temp gauge in the cluster
16 - oil pressure light (pretty sure this was affecting the oil light in the cluster)

The following made no difference on my car
2 - oil static
15 - oil dynamic
17 - si board



end of part 1

Part 2.

Now, on the passenger side there is also a white 3 pin connector. It's got a black, green, and yellow/white (yellow/brown) wires.





will not start



connect the green and it will start but no tach or mpg





connect the black and you'll get the tach, connect the yellow and you'll get mpg









If the green wire is not connected, car will crank but will not start.
If the green wire is the only one connected, car will start but you'll have no tach or mpg, speedo will work though
If the black wire is connected then you get tach
If the yellow/white or yellow/brown is connected then you also get MPG

Hope this helps.

[RickSloan]

jean this is gold, thank you for taking the time!

any word on how to make the tach work with the motronic 1.3 harness?

[Jean]

You are welcome. To confirm, the green wire does not have to be connected. With the B35 harness it will start right up w/o the green wire, it must be a requirement with the e30 harness.

To get the tach working, you'll need to run a wire form the b35 harness to the black wire. Look at my other thread where I took the harness apart, and I am pretty sure I made a post there. If not, I'll look tomorrow and tell you for sure which pin from the b35 side I am using for tach.

[wildstoats]

This needs Sticky'd! Awesome post man!

[RickSloan]

for reference to get the tach working you can cut and splice the only all black small wire coming out of the ecu and attach it to the black wire mentioned above.

This wire runs to a pin on the b35 harness that doesnt see anything on the e30 side

[flawdaboi407]

can you clear up where to connect the white mpg wire? good post!

[martijn76]

Old topic, but this could be the problem with my build.
Im using a '88 m20 loom on a m30 engine in a 1986 325i.
The engine turns on the starter but won't go, it get's no petrol.
The green wire in the glovecompartimentbox, what should it be connected to? I thought only the other two wires should be plugged in since I'm using a newer modell loom, but I hope I'm wrong, this is an easy fix.
Thanks.