SI board woes!

[moncon]

So my speedo stopped working. I checked the sensor at the diff, and the wiring, and it seemed okay to me. When I tap the dashboard the speedo jumps. I removed the SI board, replaced the batteries with Varta rechargeable NI-MH 800 mAh batteries (got an auto-electrician to solder them nicely for me). Now the speedo works when I start driving, but stops working shortly afterwards. Also, the rev counter doesn't work at all anymore (it was fine before). Fuel and temp gauges working. Service lights on. I saw this on the Wiki:

"However, if you have fitted new SI batteries and you're still having rev counter issues, then its worth looking for the signal feed between the dash clocks and the ECU. The ECU pumps out a square-wave signal to the dash, so you can't check it with a regular multimeter, but you can check that the signal wire is in good condition between the clocks and the ECU. This is a black wire that, on Motronic 1.3 vehicles, runs from ECU pin 6 through the C101 plug pin 7 to the dash cluster's blue plug pin 7. Most likely, there is corrosion on the C101 plug which is affecting the signal, or the C101 isn't screwed together properly."

That sounds a bit more than I could deal with myself so I would take it to the auto-electrician in that case, but perhaps there is something else (and something more simple?!) going on? Also, I don't know why the speedo would work for 5-10 minutes when I start driving and then stop working. My car is a 1988 318i.

Cheers!

[RKB]

Have you checked the soldering on the back of the Speedo? Mine came back to life after I re soldered the connections.

[moncon]

Good idea, I’ll try that this afternoon, thanks !