Please help with potential short circuit in car

[JHZR2]

Hi,

Last weekend I was working on the door speaker on my 1991 BMW 318i. After I finished, I started up the car, and my tachometer and clock werent working. I did quite a bit of research, and have since done some tests for continuity, etc.

What happened was that for some reason, a lot of power is going through wires that arent supposed to be getting so much. Causing the PCB to burn out, and when bypassed, the fuse to pop.

To make a long story short, the power for the clock comes from a continuous 12V that goes through the instrument cluster. Since whatever went wrong has, it burned out the trace on the PCB inside the cluster. If I jumper the input to output, bypassing the cluster, then the main fuse for the circuit blows (the conductive film on the PCB was the first thing to go, and acted like a fuse of sorts in this situation).

The line between where the harness gets power from my cluster, and where it attaches to the clock has a resistance of 0. If I dont attach the clock to the correct end of the harness, the fuse will still blow when jumpered, indicating that the problem is in the wiring, not the clock itself.

I guess what Id like to know is, can you still have a short circuit, if your wiring exhibits a resistance of 0, indicating properly operating wiring?

Thanks for your help,

JMH

 

[dkcase]

If I follow this description, check the resistance from the end of the wire to Ground. if that is zero, or anything but infinite, there is a short circuit to Ground along that route.

I think even if there is short circuit to ground along the route of the wire it will still show 0 ohms continuity between the ends.

You know of course that the voltage needs to be off while doing these resistance measurements.

 

[JHZR2]

If Im getting what youre saying correct, if I test between the end of the wire and ground, and there is a short, itll show continuity because both the end Im using for testing, and the other end (where it shorts to ground) are both obviously connecting to the ground, due to the problem in the wire, correct?

If for some reason it isnt shorting to ground, if I put a voltmeter from one of the ends of the wire to ground, I ought to see 12V (or some voltage), right?

Will I have to check for shorts from both ends? I assume not, since the wire is still continuous as per the 0 ohm resistance.

Thanks again,

JMH

 

[dkcase]

m-m-m-m

I think that sounds right..

THere should not be continuity from the end of the wire to ground. THere should be the proper voltage difference (We are saying 12 V) between there and ground.

 

[Gary Allan]

What else is attached to the harness? If you blow the fuse when 12v is attached to it ..it's finding ground. Unplug everything attached to the harness. Attach items one at a time. When the fuse blows ..you've found your shorted item. If it blows when nothing is attached to it ..the harness has a naked wire touching ground.