RPM Gauge dead I've been doing a new dash install job on my '90 E30; did a test run two weeks ago to verify that all gauges were working and they were. Today I was at it again trying to put all of the remaining trim back in place and I discovered the battery was dead. Didn't think much of it - the car has hardly been run all winter. I jumped it with my truck and in the process of working on the trim I realized that the RPM gauge was no longer working. I checked fuses 10, 12, 21 per Bentleys and soaked all the harnesses on the back of the instrument cluster with DeOxit. SI batteries test @ 3v so they are not dead but I suppose the board could be fried from jumping the car? Not sure what else to do other than check for ground and continuity; wanted to hopefully get some advice as well. Thanks. PS the speedo may be dead as well; I can't drive the car right now to verify.
It sounds as if the only thing that's happened since the last time the tach worked is that the battery ran down. If that is the case, I'd suspect the SI board. I'm not positive, but I think you should see 3.6v if the batteries are good.
I agree with the post above. I had a battery go flat in my last E30 and it managed to kill the SI batteries. My multi-meter measured decent voltage on the batteries but they either would not charge or hold a charge and replacement cured my dead tach. and temp. gauges. Matt
SI Battery Voltage I believe your SI Board only has two AA batteries wired in series (I checked on realoem.com), so that means total voltage should be about 2.4v with either NiCad (original) or NiMH (replacement) batteries. The voltage to the batteries (when being charged by the system) would be higher than this, but I've never measured. If you're interested, I wrote an article in the May 2007 Roundel ("Move 'Em Out!") giving instructions on how to move the batteries off the SI Board and to an easily accessable place. Its a good idea since soldering batteries is dangerous and is tramatic to a sad 20 year old circuit board.
