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Old 09-19-2020, 07:45 PM   #1
Habusailor
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Default Electric short somewhere

Just need to rant a bit. My 49 shoebox, 4 dr. Custom, I have a short somewhere. The fuse on the tail lights and dash lights blows after a few seconds of turning on the lights. Headlights stay on.

Itís the fuse just above the ignition switch.


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Old 09-19-2020, 08:24 PM   #2
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Default Re: Electric short somewhere

On the wiring diagram it looks like the tail lights and the gauge lights are two separate wires. Might try taking them loose and then touch one at a time back to the fuse and see if you can isolate which circuit it is.
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Old 09-20-2020, 07:44 AM   #3
Habusailor
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Default Re: Electric short somewhere

I thought that too but my wiring diagram is a bit fussy. But they obviously get power through the same fuse. There are 2 fuses side by side under the dash, above the ignition switch. The fuse on the right (passenger side) is the one that blows.


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Old 09-20-2020, 09:51 AM   #4
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Default Re: Electric short somewhere

Separate the wires coming out of the fuse as mentioned. Had the same problem with my 49. It was the wiring junction at the left rear frame area, that connected to the wiring going up to the lights. (woodie) I also have the factory turn signals. The insulation back there can get worn away and cause grounding. Also did away with the brake light switch on the MC, and have used a mechanical switch with zero problems.
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Old 09-20-2020, 09:56 AM   #5
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Default Re: Electric short somewhere

How old is your wiring?
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Old 09-20-2020, 10:36 AM   #6
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This is how I read the wiring diagram. Might start by disconnecting the input to the light switch that comes from the fuse on the CB panel. If that is OK, then remove the output of the light switch to the gauge lights and tail lights one at a time and see if you can isolate the circuit.

The tail light wire should be Black and the gauge wire Black/Red.

The wire between the fuse and the light SW should be Yellow/Red.
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Old 09-20-2020, 11:14 AM   #7
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Default Re: Electric short somewhere

The old resin and cloth covered wire that was used in the early Ford days can crumble to dust after so much time. It's not unusual to have opens or broken wires, shorts to ground, and cross shorting from one wire to another. Shorts to ground and cross shorts can both cause a circuit protective fuse to blow. It sounds like the OP has a problem of that nature.

Dash lights are usually controlled for dimming through the main light switch but there may be a light for the key switch or a light in the glove box. I'm not sure about dimming on the 49 & 50 Fords though since my experience is mostly with the Mercury cars. In any case, the wires with the most exposure to the elements are the ones to check first. The tail and stop light wires travel all the way to the back of the car and can be exposed to some moisture and may run close to a lot of structure that will act as a ground path. If specific wires are isolated by disconnecting them at both ends of the circuit, it's easy to check them for shorts to ground with an ohms meter. Cross shorting depends on the circuits each wire is in a run with so it takes more time to find. It may be easier to replace the electrical harnesses for the circuits that are having problems and especially if the insulation is in poor condition. Harnesses are available from several sources.

For disconneting the terminal blocks that Ford used in the 8BA era, a person can generally find a tool that can be wedged into the gap of a socket to aid in removing the pin from the socket. They can be stuck in there pretty good but I've always managed to get the pins out without breaking the wire.

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Old 09-20-2020, 04:36 PM   #8
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Default Re: Electric short somewhere

I had issues with my shoebox Ford lights and that was in 1964. The car was only 14 years old but had seen a lot of NY winters, I had to replace/add a few grounds, and being a young whipper snapper I spliced a few also.
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Old 09-20-2020, 04:45 PM   #9
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Old 09-20-2020, 10:55 PM   #10
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Default Re: Electric short somewhere

'Somewhere' is likely to be where the wires pass through a bulkhead. Pay attention to those places in the body where wires go from drivers area under dash, making their way on the drivers side from front to the rear lights. Worst comes, use a new wire to replace the errant shorty one...just which is least time consuming, replacing or finding and fixing.
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