Rev Counter wiring issues

[chaosss]

Hi,

I modified my wiring loom on my 1990 318is (you can see where this is going ) to remove a lot of the stuff I didn't need anymore (this includes all interior lighting, central locking, electric windows etc. etc.)

Now when I bolted it all back together my rev counter (+ economy meter) no longer works (but everything else does).

I tried a different cluster and that didn't make any difference so I have obviously balsed something up. I have also checked fuses 10 & 21 and they are fine.

Now I see a lot about the black wire on the C101 connector. Just to be sure is the C101 connector the big multiplug by the fusebox in the engine bay (i.e. the one that you plug the service reset tools into etc) or is it somewhere else?

Also what about the white multiplug just by where the main loom enters the car (inside the car). Would this have anything to do with it?

What wires can I get a voltmeter onto to check where the signal for engine speed is reaching and what sort of readings should I be expecting. I believe engine speed comes from Pin #74 (off the top of my head) on the ECU but whats an easy way to test this (and diagnose which pin is which)

I downloaded some wiring diagrams but didn't know where to start really.

Thanks

[Brianmoooore]

C101 is the big plug and socket by the fusebox, but I hope you don't try to plug in your service reset tool in here!
Nothing to do with the connectors behind the dash either.
Engine speed signal comes from the ECU on a black wire (probably pin 74, as you say), goes through the C101, down through the tube in the bottom of the fusebox, and across to pin 7 of the blue cluster plug. No other joins, and no branches.
Sure your original and replacement clusters have good SI boards?
The engine speed signal will be some kind of square wave, I imagine, but I've never put a 'scope or AC volmeter on it.

[chaosss]

Thanks Brian.

Will hopefully start having a look next week.

[oze30]

if I was to get an aftermarket tacho, how/where could I wire it up to? Sorry for O/T but mines stuffed aswell!

[Brianmoooore]

if I was to get an aftermarket tacho, how/where could I wire it up to? !

However the instructions that come with it say.
Sorting the OE one would be easier!