Gerald cook
Member
I have a 12 volt system with and alternator do I need a fuse for the alternator.
Any help would be appreciated thanks. Jerry
Any help would be appreciated thanks. Jerry
Fuse for alternator
- Thread starter Gerald cook
- Start date
Jim/GA
Well-known member
Yes. A few strategically placed fuses will help protect your car's wiring harness from unexpected shorts. The protective value is the same if you have a generator or an alternator. The battery is capable of putting out a LOT of amps if you have a short.
Coming out of the alternator, it is good to have a fuse to protect the main wire into the headlight switch. Figure out what your lights need and go with a fuse a bit above that. For example, 20 amps.
A fuse to protect the wire going into the horn is also a good spot. The only thing on that wire is the horn, so a 10 amp fuse should be enough.
Finally, a fuse down by the starter switch in the solid yellow wire is a good overall protection device. Something around 30 amps should be enough.
After you have the fuses in, you can adjust the amps up if any of them blow during normal operation. I don't think they will.
Coming out of the alternator, it is good to have a fuse to protect the main wire into the headlight switch. Figure out what your lights need and go with a fuse a bit above that. For example, 20 amps.
A fuse to protect the wire going into the horn is also a good spot. The only thing on that wire is the horn, so a 10 amp fuse should be enough.
Finally, a fuse down by the starter switch in the solid yellow wire is a good overall protection device. Something around 30 amps should be enough.
After you have the fuses in, you can adjust the amps up if any of them blow during normal operation. I don't think they will.
Y-Blockhead
Well-known member
Jim gives very good advice. Smoke is hard to get back into wires once released. I also have fuses on my turn signals and auxiliary phone charger/GPS plug.
I added a fuse box on the back side of my junction box.
I added a fuse box on the back side of my junction box.
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Mel Larsen
Member
I just had a question pop into my poor old skull. The 29 A I just bought yesterday, and haven't been able to mess with because of some very nasty weather, has been converted to 12volt. Would they have kept it positive ground. I might have to put red tags all over the electrical system. Positive ground just seems wrong to me.
Y-Blockhead
Well-known member
More than likely when they converted it to 12v they also made it negative ground but I suggest you check it closely.
Mel Larsen
Member
I will first thing in the morning, thanks
katy
Well-known member
You don't need a fuse for the alternator, but other fuses as Jim (post #2) suggested is a very good idea.
rotorwrench
Well-known member
The alternator has it's own internal protection but it's not infallible. The buss that connects the battery to all other components should have a protective device to save the wiring in the event of a short to ground situation. Model As have so little wiring that one fuse is generally sufficient to protect the whole system. Fuse kits are available for installation on the starter location. Your start solenoid may be in the way of such an installation but an inline fuse can be put on the affected battery to terminal box power feed wire.
I did 12 volt negative ground on mine . I used a generic 10SI GM alternator, one of the smaller amp rated ones. I put a fusible link between the alternator output and a wiring block on the engine side of the firewall. Fusible links were commonly used instead of fuses where you didn’t want fuses to blow from a momentary overload. The wiring block provides power to headlight relays and ignition switch. That is my recollection as it has been a number of years since I did the wiring.
My philosophy on wiring is to keep high amp loads out of the cab area, and to protect wiring from overloads and short circuit fires. I use relays, fuses, and fusible links liberally. I experienced an electrical fire, originating under the dash of a ‘56 Ford pickup in my youth during the 1960s. It was traumatic, but I got it under control by exiting the cab starving off the oxygen supply, with windows up and doors closed.
My philosophy on wiring is to keep high amp loads out of the cab area, and to protect wiring from overloads and short circuit fires. I use relays, fuses, and fusible links liberally. I experienced an electrical fire, originating under the dash of a ‘56 Ford pickup in my youth during the 1960s. It was traumatic, but I got it under control by exiting the cab starving off the oxygen supply, with windows up and doors closed.
Y-Blockhead
Well-known member
Fusible links are not recommended by Ron Francis Wiring. They suggest using a Maxi-fuse instead. Here is a page from their catalog.
I use a 50 amp Maxi-fuses on my '55 Ranchwagon
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Y-Blockhead: regarding fusible links. Such links should only be used outside of the cab so any link that burns while doing its job will not expose occupants to significant smoke and fumes. The Ron Francis Wiring company has its own product competing with the low cost, easy to install fusible links. Fusible links are sold in most auto parts stores in several ampere ratings.
Y-Blockhead
Well-known member
Have at it, my friend. Anything that “burns while doing it’s job" is not for me. Anything around that burning wire is going to burn too.
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