rev counter not working on M50 conversion

[booomer]

Hi guys, i have a 1990 e30 coupe that was originally a 316i but now has a 1991 non-vanos m50b25 in it from an e34. The problem is that the rev counter is not working since the conversion, it worked before but now does not move. As far as i can make out the black wire from the m50 loom should connect to the black wire that goes to pin 9 on the e30 plug. This is how i have mine wired but still nothing...help

[e30-EVN]

Pin 20 black to pin 9 black so you have that right.
Have you lost any other instruments mate? Check fuse 10

[booomer]

The mpg clock thing doesn't work but i was under the impression that this would throw a wobbler because of the different signal going to it. all the other guages work ok. i have just checked behind the instrument cluster and the black wire is still showing the same signal as it is at the loom/body plug so maybe its the rev counter its self?

[Brianmoooore]

316i E30 tacho should work OK driven by a M50 ECU, connected as you describe, but will need a 6 pot coding plug in the front to get it to read right.

[booomer]

right so even without the correct coding plug there should still be some movement?

[E30BeemerLad]

right so even without the correct coding plug there should still be some movement?

yes

[booomer]

mmm, any other suggestions? any way of testing the gauge or if its getting the correct signal etc?

[booomer]

someonemust have experienced this

[Brianmoooore]

Not much more we can do from here! Signal leaves ECU on black wire. Black wire goes to instrument cluster, and drives tacho.
No common faults associated with this, other than the tacho can be affected by failing batteries on SI boards that use NiCd ones, and the signal is sensitive to poor connections on the black wire.
Trying another cluster would be the obvious next move.