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.

 

Never had that problem, but since the reverse lights are on that circuit, I'd start with the wiring to the trunk lid, where it bends. It follows the drivers side hinge. A short there would blow the fuse.
Passenger side hinge is a vacuum hose to the trunk lock for the central locking.

 

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?

Thanks, Ian.

 

Vehicle speed sensor or distance sensor is on the drivers side of transaxle/, accessible from engine compartment. in the vicinity of the drivers side inner CV joint.

 

Yes, I see a sensor there, thanks a lot Rhibdrivr... I will check it out (when my son brings the silly car back next weekend...)

Ian

 

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.

Thanks to all for locating this device...

Cheers, Ian

 

sweet!
You don't happen to have the pinouts for the Motronic ECU, do you? Doing a little project and need to find a couple of signals.

 

George, I now have a Bentley Manual, I will try to scan in Motronic ECU Pinouts over the weekend, post. Not sure what day, will try to be as quick as possible...

To be correct, what model car are we talking about. the manual covers several?

Cheers, Ian

 

Same as yours, I think...1988 90 4cyl FWD auto. I checked the Bentley manual, only pins listed are the ones that are actually connected, I need to find a "fuel consumption" signal for a trip computer. Basically, it's a low voltage (.3-.8V: higher volts=more theoretical fuel consumption) that the trip computer needs and I am trying to figure out if the signal is there or if I need to look elsewhere. No hurry, no worries.

 

George, I have the same Bentley manual, and you are correct, for your purpose, it show only those signals active in that car. Sorry I could not be of more help. Good luck with your project.