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Old 09-24-2019, 01:43 AM   #1
Neil Mylar LakewoodCA
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Default Trying to find the source of a blown starter fuse.

I own a 1929 Model A Briggs body pickup. I purchased it from the family of a deceased friend. I had been told that
there was a short, possibly in the headlights that caused the starter fuse to blow.
I had the lights on during my first test drive and experienced a blown fuse. Not having time to search out the problem, I have only driven it in the daylight hours and have not turned on the lights.

I spent today, looking for the cause. First of all, the truck has an original light bundle housing, not a repo one with problems. I took it apart and it seemed fine, with no steering column oil. The wire loom assembly looks fairly new.

I checked the headlight wiring and it appeared to be fine. The wires go directly onto the headlight shell and connect to new bulb socket assemblies. I dont see any problems. There is no bullet wires plugging into the plastic holder.

Next i checked out the brake light switch. It is original too. I disassembled it and found it in good working order. It was a little oily and I removed the oil.

Finally I checked out the tail lights and brake lights and found nothing unusual.


There is a third brake light, high on the back of the cab that is not working. I'm wondering if there might be a hot wire in it that could be grounding out. Hope to check it out tomorrow.


In summary, I found nothing today that might be causing the fuse to blow, but i will keep looking.

Do any of you have some suggestions on what I might have missed?

I plan on taking it for a test drive over the weekend, with the lights on, but I'm not hopeful.

Thank you.

Neil




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Old 09-24-2019, 05:54 AM   #2
Jacksonlll
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Default Re: Trying to find the source of a blown starter fuse.

You have to establish that it is in the light circuit. Disconnect the light harness at the generator and see if all is OK. If it is, then you know it is in that circuit. Get an ohm meter with a straight pin on one end. Stick it into the wires to find out which one is shorted to ground. Good luck. Check that IP light too.
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Old 09-24-2019, 11:45 AM   #3
Badpuppy
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Default Re: Trying to find the source of a blown starter fuse.

The starter-mounted fuse is intended to protect the battery from discharging from a dead short through the generator caused by stuck cutout contacts when the engine is shut off. A short that both draws down the generator and blows a 30-amp battery fuse would seem quite an event - I assume the engine died?

Check the coutout terminals for resistance with the engine off - anything other than open indicates the cutout should be repaired or replaced. Also check behind the dash for a pinched wire or terminals shorting against the gas tank. These don't have anything to do with lighting, but worth a look.
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Old 09-25-2019, 10:49 PM   #4
Neil Mylar LakewoodCA
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Default Re: Trying to find the source of a blown starter fuse.

I've driven the truck on several occasions without having the lights on and there has been no blown fuse.

The horn works great and does not blow the fuse.

The truck has a 6 volt alternator, so there is no cutout points to get stuck.

The only time the fuse blew was when I was driving with the lights on. Having the lights on while sitting in the driveway, does not cause the fuse to blow.
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Old 09-26-2019, 05:31 AM   #5
Jacksonlll
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Default Re: Trying to find the source of a blown starter fuse.

I assume you are using a 20 amp fuse.
It must be in the light circuit. Do a visual check of the wires under the car to make sure a wire clip of something else sharp has not grounded a wire.
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Old 09-26-2019, 11:21 AM   #6
Badpuppy
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Default Re: Trying to find the source of a blown starter fuse.

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If the fault occurs in only one position - bright or dim, concentrate on the forward harness. If it happens in any position, including park (Twolite), then it will be in the taillight circuit. As JacksonIII says, check the frame clips. They can easily pinch through the harness if not carefully installed. Easy to repair with friction tape.
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