wiring loom query?

[daveyw]

got a 1991 316i touring last weekend with a knackered engine. i have fitted a 1990 325i engine. what is the 3 wire plug for that comes out of the loom near the multi plug for the ecu? the donor car was plugged in but the touring does not have anything for this to plug into?
hope this makes sense, cheers.

[kam-325i]

Which end is the Multi-Plug ? In the engine bay or under the dash...

[daveyw]

under the dash dude. the rev counter, temp gauge, leccy windows and mirrors aren't working so was wondering if it had anything to do with this plug? the lights had a mind of their own though this is to do with all the melted wires coming from the switch! would this have anything to do with the above not working? plz help, wiring is not my strong point!

[Martinaston]

If it's the black and white plug i think it's for the OBC and Auto box (not sure i'm being lazy)
If your's is a manual then just leave it.

[Martinaston]

The rev counter won't work unless you change the coding plug at the bottom of the instrument cluster.

[Martinaston]

I think this is the plug your on about ?

[daveyw]

The rev counter won't work unless you change the coding plug at the bottom of the instrument cluster.

wheres that then, behind the cluster?

[daveyw]

I think this is the plug your on about ?

looks very similiar but seems to come out of the loom about 3 inches away from the ecu multiplug

[daveyw]

there is no black plug next to it either

[daveyw]

scuse my ignorance but whats an obc?

[Martinaston]

If you remove the black strip between the steering column and the instrument cluster (it's held in by two silver thumb screws from behind, get your head in the footwell and look up untill you see them).
Once youv'e got that off you should see a white rectangular plug about an inch long below all the warning lights.
You'll have to use the one from the car the engine came from.

[Martinaston]

OBC= On Board Computer

[daveyw]

cheers dude, you're a star!

[Brianmoooore]

The rev counter won't work unless you change the coding plug at the bottom of the instrument cluster.

More accurately, the rev counter won't read correctly, sinvce it'll be now getting 3 pulse per rev rather than the 2 it should be.

[Brianmoooore]

There is normally a white socket and a black socket coming off the ECU loom, and fixed to a bracket on the LH end of the ECU.
Only ever seen anything connected to them on cars with aircon and switchable auto boxes, so if your touring has neither of these then don't worry about it.

[Brianmoooore]

under the dash dude. the rev counter, temp gauge, leccy windows and mirrors aren't working so was wondering if it had anything to do with this plug? the lights had a mind of their own though

Elecric windows, mirrors, roof and heater blower are controlled by the two unloader relays - do the latter two work?
The unloader relays K5 and K7 in the fusebox disconnect these circuits while the engine is being started, and are controlled by the black/green wire going to the smallest terminal on the starter motor.
instument panel uses fuses 10, 12 and 21 for various functions, so check these all out.
Usual rev counter problem, especially after an engine swap, is a poor connection on the black wire at pin 9 of the C101 connector on the bulkhead, next to the fusebox. (big engine loom oplug and socket)
No temp gauge is unusual, and if its not any of the fuses above, then disconnect the connector from the brown sensor on the water outlet elbow (front, top of engine), and short the single connector in the plug to earth with the ignition on. This should make the temp gauge read full hot.