Short to ground at battery after hooking up jumper cables in reverse for 30 min. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-29-2011, 10:47 PM
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Short to ground at battery after hooking up jumper cables in reverse for 30 min.

My friend had a no-start (low battery) on his 86 F150 4x4 4.9 so he hooked jumper cables from his Crown Victoria and went inside the house for 30 min.
When he came back to the truck he realized he had hooked up the cables wrong. The Crown Vic battery and truck battery were both dead. And several wires were burned up on the truck. I was able to get his Crown Vic repaired by replacing a fuse and charging the battery.
I didn't have time to try diagnosing the truck that day. Since then, he taped up all the burnt wires and replace the alternator with a reman unit. But it still has a short to ground somewhere when he hooks up the battery cables.

I guess one thing I need is a wiring diagram for this circuit and of course any ideas on what circuit is likely to have a short to ground after having the jumper cables connected in reverse polarity.
I have not started trying to diagnose this yet but I'm about to get started now. I'll post any details I find.
Thanks for any help!
Mike

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Old 07-30-2011, 02:46 AM
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You might want to just get a new harness Mike. Otherwise, untape all of Gomers taped up stuff and clip those wires one by one until you find it and replace any damaged wiring. In all my years wrenching I have never had that exact scenario so it's hard to say what all could be fried. My best guess is hot and ground wires melted together in the harness somewhere.
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Old 07-30-2011, 06:29 AM
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Quote:
Originally Posted by willowbilly3
In all my years wrenching I have never had that exact scenario so it's hard to say what all could be fried.
Me either
I found a short within the starter solenoid so far. When I connected a known good battery (with ignition key in off position), the starter engaged., And after disconnecting the wire that energizes the starter relay coil, the starter still engaged.

And the battery is drawing way too many amps (50) on my charger and kicking out the thermal overload (charging battery alone with no cables hook to it), So I'll get a solenoid and battery tomorrow and go from there.

I hope this is all that's screwed up - but we'll see. Hopefully I won't have to go back through everything Gomer did too.
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Old 07-30-2011, 09:40 AM
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You know a battery will charge backwards. It's possible that has happened. That would explain the charger going to full tilt and kicking out. It might also explain the solenoid staying engaged but I can't quite wrap my brain around that to say for sure.
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Old 07-30-2011, 12:31 PM
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My brother's girlfriend's kid put a in battery backwards in my brother's 1976 Ford F250 highboy and it was a major deal to fix. It blew out just about everything electrical. I think you might be facing a major redo on an 86's electrical system which would be more complicated than a 76.
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Old 07-31-2011, 06:42 PM
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Quote:
Originally Posted by mike 96 ws6
... Hopefully I won't have to go back through everything Gomer did too.
I wouldn't count on it. Just wrapping tape around them is not sufficient. Wiring that got hot enough to melt the insulation may well be damaged beyond repair. Not only may there be wires melted together and shorting, but some of the wire strands may have melted/vaporized, leaving the cable with a lower than original capacity.
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Old 08-02-2011, 12:45 AM
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I replaced the starter solenoid and battery and it fired up and ran fine. Alternator is charging too. So he's happy for now but I told him not to count on those taped up wires for long. His income is a limited disability check so he said he would pay me to get all the wires replaced when he can afford it.

Thanks for the help everyone!
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