SO, my latest problem is the #12 Fuse blowing, at first once every month or so, now hard short. This results in no insruments, trip odometer, odometer, backup lights etc. I have (finally) ordered a Bentley Manual, but just thought I would put this query out in case someone had a similar experience... any idea where to start looking for the short?
Once I get the manual, it will be leg work to trace the various paths from Fuse #12... still, not something I really look forward to...
Any insight or similar experience would be most helpful and appreciated.
OK, traced trouble to one of two wires coming off the large black connector in the middle of the bottom of the main fuse panel in the engine compartment. Cut the offending wire with the short, now all works perfectly, fuse does not blow, but (of course) the Speedometer is dead, so I am pretty sure it is the Speedometer sending unit (sensor) or wire run thereof. Unfortunately, I do not have my Bentley manual yet, anyone have any idea where this sender/sensor would be located?
Problem fixed - wiring short near Speed Sensor, cleaned up, taped, also cleaned / tested Speed Sensor.
Information for others:
This sensor is a 3 wire active device, 12 volts in, ground and centre pin is signal out, apparently an open collector pull down to ground - to test connect 12 volts, ground, then pull up the centre terminal to 12 volts with a 10 K (value not too important) resistor. Centre signal terminal should be a square wave (0-12v-0) as the sensor gear wheel is turned. The output can be observed using a meter or better, an oscilloscope... Sensor couples to an internally mounted gear that turns as the driver's side wheel turns.
Printable Version
1988 Audi 90 Fuse #12 blows... - 
