E30 M50: C103 wiring

[MaxBell]

Hey guys;

I'm getting really frustrated with my swap not working (3500 rpm limp mode cut off), but I wanted to confirm that the C103 is wired properly.

I have engine speed (a black wire from the M50) wired to Pin 1.
I have nothing wired to Pin 1.
I have fuel rate (a yellow/white wire from the M50) wired to Pin 3.

I was looking at some swap wiring diagrams and one says that I have to wire Pin 2, to prevent a 3500 rpm cut off?

Also: could the VSS be the problem here? How do I wire the VSS for my M50TUB25?

[FredK]

No. Pin 2 does not need to be hooked up.

The 3 pin connector in your glovebox is called C104.

You pull the VSS by splicing into pin 26 on C3, the yellow connector on the back of the cluster.

[MaxBell]

Whoa, I've heard nothing about splicing the VSS? What do I connect that to?

[FredK]

You need to connect the E30 VSS signal to pin 14 on the E36 wiring harness.

A lack of a vehicle speed signal is likely unrelated to your bogging and stumbling problem, but it's just something to hook up, if you haven't.

[cormier]

Not to thread jack but I'll put input here

I haven't hooked up VSS either, the Treehouse harness says its "behind the glove box" with the tach and fuel rate wires as well (in that 3 prong connector I'm assuming)

I don't think VSS would help you greatly either, but one more thing to hook up nonetheless
The three extra connections that don't go through c101

road speed to brown/red wire
Fuel rate to yellow/white wire
Tachometer to black wire

All listed behind glove box, and for an early model

Edit again: from reading around, it seems like treehouse screwed up and the brn/red wire for VSS needs to be spliced behind the cluster off the yellow plug and not behind the glove box in c104 with the other two.

[328ijunkie]

VSS typically causes a 5500 rpm cut.

[e30_325es]

Not to thread jack but I'll put input here

I haven't hooked up VSS either, the Treehouse harness says its "behind the glove box" with the tach and fuel rate wires as well (in that 3 prong connector I'm assuming)

I don't think VSS would help you greatly either, but one more thing to hook up nonetheless
The three extra connections that don't go through c101

road speed to brown/red wire
Fuel rate to yellow/white wire
Tachometer to black wire

All listed behind glove box, and for an early model

Edit again: from reading around, it seems like treehouse screwed up and the brn/red wire for VSS needs to be spliced behind the cluster off the yellow plug and not behind the glove box in c104 with the other two.

What color, and where do I find, the wires that are road speed, fuel rate, and tach?

[JayGotti]

[QUOTE=FredK;3342705]You need to connect the E30 VSS signal to pin 14 on the E36 wiring harness.

A lack of a vehicle speed signal is likely unrelated to your bogging and stumbling problem, but it's just something to hook up, if you haven't.[/QUOTE


so what your saying is pin 26 on the c103 goes to pin 14 on the harness? will this stop the 4k cut on a m50 swap?

[328ijunkie]

^No and yes. C103 has 3 pins. 26?

[FredK]

Pin 26 on C3, the yellow plug that plugs into the cluster.

[MaxBell]

How to wire VSS up on an M50. Ok, so just to confirm before I blow anything up...

I should wire Pin 26 of the yellow plug into Pin 14 of the X20 (signal will be coming from the engine side). Now do I cut the Pin 26 out of the back of the cluster? Am I trying to send the signal from the engine into the cluster, or into the DME (which plugs into the cluster)

The Yellow Plug





The X20 (M50TUB25)



Does this look proper?

[frankie591]

How to wire VSS up on an M50. Ok, so just to confirm before I blow anything up...

I should wire Pin 26 of the yellow plug into Pin 14 of the X20 (signal will be coming from the engine side). Now do I cut the Pin 26 out of the back of the cluster? Am I trying to send the signal from the engine into the cluster, or into the DME (which plugs into the cluster)

The Yellow Plug

The X20 (M50TUB25)

Does this look proper?

No you need to use the wire on the plug that plugs into that socket. Pin 26 should be a brown/red wire in one of the corners. Just t-splice into that wire, and connect it to pin 14 on the engine harness. The signal will come from the c3 pin 26, into pin 14 of the x20 and tell your ecu how fast the vehicle is travelling.