39 Ford blowing fuses

[mjdunn]

I purchased my 1939 Ford DeLuxe Tudor (6 volt) just 4 months ago. It has been blowing the 20 amp fuse that serves the Headlights, tail lights, brake lights, dome light & horn. It does not blow right away, but after it is driven with the lights on for an hour or two. The previous owner had put halagon bulbs in the tail lights and I thought they were drawing too much juice because the headlights would dim about 50% when the brake lights came on.

I changed the bulbs to the original type (3 candle power) and the headlights no longer dimmed and they were brighter. However, the fuse still blew a few days after installing the new bulbs. I have run out of ideas as to what would be causing this. What about trying a 25 amp fuse?

[FL&WVMIKE]

You probably have a bad connection, somewhere in your system. Check to see if you have any badly corroded connections. You might have a short somewhere too. Feel your wiring to see if you have any HOT spots. You might have a too thin wire, somewhere.
MIKE

[Terry,OH]

The fuse should NOT protect the horn, if it does get the horn circuit off the fuse. It is only on the light circuits. The horn circuit draws nearly 18 Amps itself. Don't go to a larger fuse! The full load through the fuse should only be about 1/2 the fuse rating.

[rotorwrench]

A 12 gauge wire needs a 20 amp fuse to be properly protected. Higher than normal resistance in a circuit makes heat. If wiring is in good condition, you need to clean all terminal connections and all ground path connections. If the wiring is very old, you may have to consider replacing either the bad wires or the whole harness. The old light switches on the bottom of the steering column can get crusty and cause high circuit resistance. Brake light switches are mounted low and they get crusty too. Cars that have weathered a lot may have problems with ground paths from the body and fender connections to the frame connections. All this stuff can have an effect.

[bluardun]

All the above is good advise; especially about DO NOT use a higher rated amperage fuse.
I would suggest inspecting or replacing the origional wire connectors. The wires are terminated with a male terminal, which plugs into a rubber covered female connector. The rubber around the connector with age detoriates. Age can effect the oxidation of the connections, causing a higher ohm rating for the current to pass thru, or a slight short to ground. Same for the light sockets, and ground connections. Clean them with fine steel wool. Not a big project, but worth your time and effort. When you find the problem it will be a small thing. Thanks for fuses; they prevent fires.
have fun

[mjdunn]

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From all of the above and my observations I think there is some wiring I need to replace. What is a good source for wiring harnesses? Thanks for all your help.

[rotorwrench]

Rhode Island Wire has the best stuff that I am aware of. They laquer coat their finished wire. They make it the way it was made in Henry's day but it is expensive with all the hand work that goes into them. A person will pay near the same price for a harness assembly that is not laquer coated but still cloth covered.

There are others that make modern type wire harnesses that are one size fits all but it is up the the individual what he wants to put in his vehicle.

[mjdunn]

Rotorwrench, thank you for the source. I will check it out.