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Old 09-08-2019, 07:43 PM   #1
Tveditr
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Default Short circuit issues. Where to start

I am new to Ford Model A’s. Most of my time has been around British cars. I am having a short problem which is draining the battery. Main fuse by starter motor gets excessively hot as did the horn before I disconnected. There is an aftermarket fuse box which I need to disconnect from firewall since it doesn’t open from the front. My question is are there any usual spots I should look for shorts to be happening? This is a 1930 Model A coupe with cowl lights. This car has not been restored. Rubs and drives well when battery has enough charge to start. This car is still a 6 volt system. Need to find a 6 volt test light. Any help appreciated.
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Old 09-08-2019, 08:07 PM   #2
wmws
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Default Re: Short circuit issues. Where to start

A 12 volt test light will work just fine. Just a little dim. Or use a multimeter. Disconnect one set of wires at a time. Headlights, tail lights, brake lights, ammeter etc. until you find the one causing the problem.
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Old 09-08-2019, 10:09 PM   #3
Tom Wesenberg
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Default Re: Short circuit issues. Where to start

If the horn is getting hot, then it's likely shorted to ground.
What does the ammeter read with the key off?
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Old 09-08-2019, 10:10 PM   #4
Mike V. Florida
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Default Re: Short circuit issues. Where to start

The biggest problem is we don't (and it seems you don't ) exactly how the car was wired.


If it were me I would turn everything off. I would disconnect the output of a terminal on the fuse panel. Connect one lead of a test lamp or meter to that point. The other lead to the wire just disconnected. The the lamp or meter will indicate voltage if there is a short.
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Old 09-09-2019, 10:04 AM   #5
Patrick L.
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Default Re: Short circuit issues. Where to start

If you are used to Lucas Electrics then the Model A is childs play.

As in any electrical system, A meter or test light [ 12v light will work fine] across a load [ battery, fuse, etc] will show if there is a draw or not.

From your post I think the first to disconnect/check is the horn
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Old 09-09-2019, 02:01 PM   #6
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Default Re: Short circuit issues. Where to start

My horn got hot when I first installed a battery and I also noticed a spark when I connected the battery. Turns out a wire was loose on the horn grounding out. Plugged it in where it goes and no drain and no heat on horn. You have to watch the cover as it goes on back of the horn . Good luck with yours as I hope it's that easy.
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Old 09-09-2019, 03:24 PM   #7
Tom Endy
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Default Re: Short circuit issues. Where to start

See attached article.

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Old 09-09-2019, 05:33 PM   #8
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Default Re: Short circuit issues. Where to start

Quote:
Originally Posted by Patrick L. View Post
If you are used to Lucas Electrics then the Model A is childs play.

As in any electrical system, A meter or test light [ 12v light will work fine] across a load [ battery, fuse, etc] will show if there is a draw or not.

From your post I think the first to disconnect/check is the horn
When I started reading this thread, I knew someone would bring up that old crock. I am not a fan of British cars but the Lucas system was waaay ahead of anything I've ever seen on any American car, even the new ones. All you need to know is what the colours mean.
As for the OP, I'd go around all of the circiuts, disconnecting one at a time (in this one, I'd statrt with the horn) and see which one results in no blown fuse. Then I'd trace the circuit right through, inch by inch, looking for the short.
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Old 09-10-2019, 03:55 PM   #9
barkleydave
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Default Re: Short circuit issues. Where to start

I have both British cars and A's Lucas is fine... it boils down to clean grounds and good clean connections to battery etc. I have a owned a MGA for 20 years and not a single electrical failure except batteries wore out..
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