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Placing a fuse in my wire circuit.

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My 29 Dodge truck has metal clad wires. I would like to avoid any short circuit since the original circuit does not have a fuse. 

I have a 15 amp fuse now and have been blowing the fuse. If this is too small the  horn maybe the problem.

What size fuse should I use?


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Does the fuse you placed in the circuit only blow when you operate the horn?

Also where in the circuit did you place the fuse?

As to what size fuse to use it depends on what and how many circuits you are trying to protect and how much current flows through those circuits when they are operating at the same time.

IE driving with the lights on and blowing the horn at the same time - the combined current draw may be more than 15 amps.

If you are only using one fuse to protect everything you need to know the total normal combined current draw of the circuit /s you are trying to protect.

Then you will know what size fuse is required.


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The horn will draw a lot of current on its own. looking at your wiring diagram it would appear that ALL your electrics are on one main fuse. Based on my experience with a 28 Chrysler with similar wiring set up, I would recommend using a 35 amp fuse.

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A few thoughts;

As your 29 Dodge originally came without a fuse maybe the engineers did not think one was needed [ Trying to protect all circuits with one fuse has it own set of challenges]

Running the cables in metal conduit offers the wiring a lot of protection from abrasive damage etc. little chance of exposed wires shorting out. 

Has your vehicle been rewired or is it the original 90 year old wires ?

Looking at the second wiring diagram the fuse block is in the main feed line therefore all current flows through this including charging current from the generator back to the battery.

Generally the fuse block would be placed in the circuit that powers the lights and horn, the generator /cut out would have its own circuit not fused.

Maybe a well placed battery isolation switch that can be easily accessed would be a good thing to do.

Also if you suspect the horn as being the cause of the fuse blowing just fit a temporary fuse in the power supply to the horn [ as close to the horn as possible]

If this fuse blows it confirms the horn is causing the problem.

Good luck

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Thanks for all your comments. Forum is a great source for information on restoring these old ones.


The wires are replacements. I was fortunate to have good patterns from my old truck so I build my wire circuits.

The only concern I have with the metal shield is that you must be very careful to isolate all the terminal connections to assure no short circuits and replacing burn out wires.. 

I suspected the horn as a problem and will try another fuse. 

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