Diagnosing a short at end of conductor

JHZR2

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I have an underhood light and a second wire with a female spade underhood. I probed it with my meter to the battery, measured 4V to one terminal on the battery, -8V probed to the other terminal.

This seems to me that we have a voltage divider with two different resistances on either side, one twice or the other.

Question becomes, what is the best way to trace the location of the short that is causing this, when the wires are caught up in harnesses under the dash?

I think it must be some sort of supplemental underhood light or something. There is no functionality I miss, no fuses open. Battery holds strong at 12.7V. It is disconnected underhood. But I’d like to see where and why it is doing this.

Fortunately I’ve never had to diagnose shorts like this before. Whats the best bet to start?
 
If you only have a single female spade it was probably meant to be a switched hot wire with gnd coming from the attachment point. So there should be a switch or relay, most likely a relay because they would not normally install a switch and run the wire on a acc delete just not put the relay in. So most likely its disconnected at both ends but to be sure you can disconnect your battery and ohm the wire to chassis gnd and then ohm to the disconnected + batt cable. I would also check the fuse box for any debris around relay sockets or empty fuse sockets. You could also check to see before you disconnect things if changing your dash light brightness or turning the dome light on changes the reading. Its very strange to see a wire at a mid point voltage if there is no current draw on the circuit. Normally any exposure to batt voltage would have it reading full batt until some other load appeared and then the voltage would divide.
 
What ever you are connecting your ground of your volt meter to " IS NOT GROUND ". It has to be in part of that circuit and at or very near the junction of the middle of that voltage divider you are looking for. There is no minus supply in vehicles.
 
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Uhmn, I would remove the bulb and the end where it is plugged into the wiring harness. Give things a once over looking for dirty or green contacts. I normally eyeball things before I break out the meter.
 
If it's not draining the battery , tape it up and move on with your life . This place will run you crazy .
 
What ever you are connecting your ground of your volt meter to " IS NOT GROUND ". It has to be in part of that circuit and at or very near the junction of the middle of that voltage divider you are looking for. There is no minus supply in vehicles.
I said I measured the potential of the exposed connector to the two battery terminals. Not “ground”. There are two different potentials, +4V and -8V. That’s what struck me as strange.


I don't think you have a short. More like a high restance,close to an open.

Then why would it have two different polarities based upon what terminal I touch?
 
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