Electrical Short

WTYRONET

MEMBER
1988 FORD THUNDERBIRD
4 CYL
2WD
MANUAL
98,000 MILES

Something is causing a short in the electrical system that does not blow a fuse. I've disconnected the battery cables and ran a continuity check and have a full short between the negative and positive cables. This tends to be intermittant. What can cause this besides bad wires?

4 Replies

CARADIODOC

MECHANIC
33,925 POSTS

What's the symptom and how are you measuring the short? Do you get the same results regardless of which way the meter probes are connected? If you have 0 ohms between the battery cables, you would have one major spark when you connected them to the battery.

Caradiodoc

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Monday, January 24th, 2011 AT 7:29 PM

WTYRONET

MEMBER
3 POSTS

Thanks for your response.
I believe the early symptom, when the car is running, is that it starts missing. When the car is turned off, he battery drains and, I found if not checked, the cells are damaged. When I last thought I had it fixed, I drove it and parked. When I got back in and turned the key I got nothing at all so I opened the hood and put my hand on the battery. It was burning hot so I disconnected the negative terminal! I had the car towed home and then checked it with an ohm meter. I haven't reconnected the cables to the battery because of the short. I have seen weird instances a while back where all the gauges went haywire while driving but it would return back to normal before I had a chance to check it out.

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Monday, January 24th, 2011 AT 8:24 PM

WTYRONET

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3 POSTS

I left out that I removed the positive and negative cables from the battery and connected one probe to the positive cable and the other to the negative cable. Then one probe to the positive cable and the other to the chassis. Same results, 0 ohms.

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Monday, January 24th, 2011 AT 8:31 PM

CARADIODOC

MECHANIC
33,925 POSTS

Hmm. The only thing that could draw so much current to make the cables and battery hot are the starter or a shorted generator. The generator output wire is fused on newer cars but not on the older, more reliable stuff like I drive. (I drive an '88 too). I would start by unbolting the output wire from the back of the generator, then recheck to see if the short is gone. If the diodes short while the engine is running, alternating current will try to go into the battery which will heat up the generator and battery and would likely cause misfires and the gauges to do weird things.

Caradiodoc

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Monday, January 24th, 2011 AT 10:54 PM