87 325e fuse # 10 (7.5 amp) fault

1987 325e 2.7l stock 230kmiles manual trans. no cruise control or power sun roof. Power windows and locks. The AC has not worked since we've had the car. Engine runs well New timing belt, water pump, valve adjustment, tune up. Symptom: under normal driving circumstances gauges quit working and the heater fan completely stopped working. Inspected fuse box and determined that Fuse # 10 had opened (failed). Does anyone think that if the SI board batteries in the instrument cluster are discharged (I verified they are bad) that this would cause fuse # 10 to open? Some other things I have noticed are as follows- Back up lights were always on so I removed the bulbs to remove from circuit fed from fuse 10, when brakes are applied tach & fuel economy gauges jump into operating position for about a second and a half and the return no operation. I can feed fuse # 20 with positive voltage and get the heater fan to operate on all 4 speeds so the fan circuit is ok. Does anyone have any ideas or suggestions?

sounds like you have some bare wires somewhere and they are shorting out or you have a bad reverse switch

Fix the SI batteries. Possible a relay is not pulling in for the heater/ac.

Am going to install an easily accessible remote battery holder for the SI board and disconnect the reverse light harness connector at the transmission. Looking at the fuse designation fuse #10, 20 & 21 all work together so the bad SI board may be problem as all problems started when when the gauges stopped working. Thanks for the input. Jim

$10 says its the reverse light wires grounding out. Ask me how I know.

OK...How do you know?

Uhh...because the same thing happened to me? The only difference was that when everything went out my high beams turned on. That is still a mystery to me. But, yeah, disconnecting my reverse switch wiring fixed that problem. I've been driving around with no reverse lights for about 6 months now. Planning on getting under there this week some time.