To fuse or not to fuse?

[Kentf1003]

Building a 1940 pickup. I read an archive thread on wiring your classic and the person ended by saying that he always adds a 50 amp fuse from the wiring harness to the solenoid. But, when I checked 50 amp fuses at the auto stores, they are all 12v. The holders have wires much smaller than the original leads coming from the solenoid. Of course the original breaker (above the steering column inside) is still in place to protect the lighting. The 50, I assume, would protect against any other short.

What are your thoughts Barners? Thanks.

[Jack E/NJ]

Fuses usually don't care about volts, only amps. However, I wouldn't add this kind of circuit protection --- just another complexity that could go wrong or bite you (like losing all electrical power) at a most inconvenient time.

Jack E/NJ

[51 MERC-CT]

Hard pressed to think of a wire from the harness to the solenoid that is big enough to require a 50 amp fuse ( could be wrong ) If not a big enough wire, the wire could burn before the fuse blew.

[rotorwrench]

The OEM circuit breakers were usually enough to protect the system. A 50 or more like 35-amp fuse would work OK on cars with no circuit protection but a person would have a hard time finding the short with only one fuse. Fuses are better to protect individual circuits so you can tell right away which circuit is shorted.

[Walt Dupont--Me.]

I use a 30 amp fuse, the kind with the 2 blades, where the 10 guage wire comes from the selinoid on all my cars. For years most cars have a fuseable link from the seloniod. Walt

[Mike51Merc]

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You guys are talking about the main line from the battery to the solenoid and then to the dash, right? Not really the solenoid wire.

You could fuse it, but by the time a 50 amp fuse blows the individual wire causing the overload will probably have burned anyway.

[Zeke...PA]

I make my own harnesses and fuse everything, better safe than sorry . I have a 50 amp fuse from the solenoid to the main fuse block. Zeke

[koates]

On an original 6 volt as henry built it early ford V8 i use a heavy in line glass or blade 30 amp fuse. It is wired in the main power connection wire on the foot starter switch which goes up to the ammeter (yellow wire) on early cars 1932 to 1938. Later cars this wire is on the main battery cable terminal on the starter solenoid. Much better to have this protection in place to protect the complete wiring harness than to have a short circuit and burn up the wiring and possibly the whole vehicle. Modern cars have fusible links which do the same job. Remember early ford V8s only had one fuse under the dash which did not protect the whole wiring harness. Model A fords had no fuses and an aftermarket fuseholder on a metal bracket which mounts under the starter switch is available. Every antique car should have something like this fitted. Regards. Kevin.

[G.M.]

Your better off with heavy duty battery disconnect, not the cheap green type. G.M.

[jack orchard]

Originally Posted by Zeke...PA

I make my own harnesses and fuse everything, better safe than sorry . I have a 50 amp fuse from the solenoid to the main fuse block. Zeke

Great work, Zeke. Well thought out. Congrats, ...jack

[Carbroke]

I could see a reason for putting a fuse between the solenoid and the main fuse panel if the fused wire were running through the firewall or other panel that could become a short but to fuse that wire when it only runs along the outer firewall for a couple of feet is just not called for. As someone else said, by the time you popped that 50 amp fuse, you would already have crispy wiring elsewhere.

Fuses are to protect against shorts and against a device pulling more current than the wire is capable of supplying. If a wire never penetrates a metal wall, and is the main source of power in the vehicle, there is no reason to fuse it at all. The Fuse panel is doing the job by protecting each of the individual circuits fed.

If a main buss is going to penetrate a metal wall, better to use a fusible link as this type of protection doesn't have normal junction that can go bad over time. It's either good or it's not.

Something to keep in mind is that every junction in a wire harness is contributing to the overall resistance in a given circuit. The more junctions, the more resistance. While not as crucial in a 12 volt system, these resistances can become a significant percentage of the resistance in a circuit in a 6 volt circuit where many times there is not much room for parasitic losses. Over time heat, oxidation, corrosion, etc. can work these junctions over and they degrade in quality. Best to keep them to a minimum.

[4t8v8]

Don't fuse your headlight circuit. If it blew it could ruin your whole evening on a dark road. Factory uses an automatically re-setting breaker.

[Kurt in NJ]

As someone that has had the smoke let out of wires as the result of adding a fuse in the main feed wire when there was none in the original design I will say that some thought has to be put into modifications ---a fusible link 1 gauge size smaller than the largest wire I would consider ok if it was properly made, but I have seen many fuse holders melted and the cause of bad connections

If the fuse on the main wire at the solenoid was to go open (either by bad connection or blowing) on a generator car the generator will still generate ---but it has been dissconnected from the battery which works to limit the voltage, the battery is an electric "sponge", it tempers the generators output ---keeps it under control ----so when it gets dissconnected the voltage can go wild ---even to over 40 volts ---this will test insulation, that hard to replace smoke will hopefully be contained in the generator --as it burns up

Another place I don't like a fuse is in the ignition system ---

Many of the aftermarket fuse holders are not very good, same goes for battery dissconnect switches, I have had to work on a lot of cars towed in due to failures of "improvements", most of the burned up harnesses that I have replaced through the years have had the root cause of improper repair and modifications.

Proper routing and fastening of harnesses will prevent most problems, and if a wire melts and the wire is routed so it can't cook up anything else ---no problem---but a big fuse in the main wire won't prevent a problem in the small wire going to a domelight ---I can understand using a small amp fuse there ---one that would blow at 120% of bulb draw ---this is where thought has to be used in fusing modifications.

[koates]

Yes of course every answear above is correct, but the fact remains that if a circuit is unprotected and a short to ground happens, guess what ??? As i stated on an early ford V8 1932 to 1938 that main yellow feed wire runs through the firewall and around through the ammeter loop or terminals before it connects onto the fuse block. Ammeters on occasion fail internally and can short to ground and so to the wire can rub through the insulation on the loop type as well. You do it how you wish but take the risk. I did not suggest a 50 amp fuse. A 30 amp is ample in a STOCK 32 - 38 FORD. This fuseholder should be a heavy duty type with perfect connections. Even the gold plated types used for stereo boom boxes would be a good option. A fuseable link is good but do you carry a spare one in your tool box ? A fuse is easier to change......once you have repaired the short circuit though. Regards, Kevin.