Problem: The EML bulb should show up for a couple of seconds when the ignition is turned on. On my 750i it didn't do that anymore. And as a result the acceleration time from 0-100km/h needed to be marked on a calendar. Somehow the whole shabang was running in some sort of emergency program. The engine did run on 12 cilinders but it took forever to accelerate. My gearbox was also stuck in 3rd gear without any warning whatsoever.
Solution: I have collected a good number of e32 spares in the past. That included the speedo from a 92 735i which has the same backplate as my 91 750i. Ofcourse I could just swap codeplugs and backplates. But as I remember the cluster did have some problems. That's why it never got installed into my 86 735i to resume the count from 299 960km.
I started by measuring the resistance of the EML bulbs that are soldered into the cluster. They are soldered in parallel. So I guess if one works it's fine.
These where fine so I had to look elsewhere. As I did once see the EML light flicker on and off I thought there might be an bad track in the PCB. Ofcourse it's multilayered so it's hard to follow the track. So I measured the contacts between the white connector's Pin 16/Pin 17 (they are connected on the PCB) to the contacts above the EML bulbs. To do this you have to scratch some of the coating from the pins at the white connector.
The measurement of the 750 cluster showed an open:
And the result of the 735 cluster showed a closed circuit:
Ah-HA! So it's an open connection. The easiest way to fix that is to run a wire parallel to the original track.
And that did the job:
You might want to glue the wire in place with some hot glue to stop it from vibrating against the other contacts and slowly break the insulation.
Job Done! All there is left todo is replace some of the bulbs, top off the coolant reservoir and bring it to the dealer for an inspection :-)
Story by Johan
If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.