I want to update the wiring in my 62 Plymouth. There was not much in the way of fusible links back then. I have installed a larger alternator from stock 40amp--to larger mopar square back 78amp with an electronic voltage regulator. I'm also installing a Vintage Air AC system, and a headlight relay system....no electric cooling fans, or high amp stereo. I was thinking of using the MIDI type slow blow fuses But I'm unsure just where to install them to protect the wiring. I was hoping that someone with more electrical backround could point me in the right direction...and maybe a wiring diagram. I would prefer not to use " fusible links" but would not rule them out. Give me your thoughts of a good plan.
He's not talking about replacing the fuse panel. He wants to add a few new circuits to the car, and protect them properly with fuses...but since things like the alternator wire handles more current than normal fuses can handle, he wants to use the screw in MIDI fuses, which require a special holder. First step would be to figure out what size wires will be needed to handle the current, then size the fuses accordingly. And maybe find Crazy Steve's Wiring 101 thread, to help you get even more confused
What do you want to protect? If you're not replacing the OEM fuse panel, what size wire is supplying it? I'm not a fan of those as it's nearly impossible to size them right when accounting for intermittent current loads. Big enough to withstand those and they end up being too big for the wire size, i.e. no protection. So here's what I'll recommend... If you're using OEM-type sealed beams, no relay is needed, the stock wiring is adequate. Only if you upgrade to aftermarket lens/lamp assemblies with 60 watt high beams will you need to use a relay. As to the AC, connect that at the same point your alternator wire is connected to the harness. Use either a fuse or circuit breaker, sized as recommended by VA at that point. Vintage Air doesn't recommend connection at fuse panels because of these limitations. For a fuller explanation, read my Wiring 101 post.
I'm replacing the alternator 12ga wire with an 8ga wire. I'm also bypassing to stock amp gauge and installing a volt meter. I am also adding a vintage roebeck 4way flasher system. , aftermarket stereo. some extra interior lights. ( and like I said before a vintage air ac system, there will NOT be an electric engine cooling fan.) In 62 plymouth had fusible links in the wiring at the mechanical voltage regulator ( but since I'm using the larger 78amp alternator I will be using a electronic voltage regulator, with new wiring cuircutt. The rest of the car is stock. But since it has limited wiring protection I want to improve on that. The wire that goes to the fuse panel is the stock 12ga wire/ to the stock 62 fuse panel. If the MIDI fuses are not a good choice, I'm open for other ideas. As for the headlight relay harness. I was just going to do that for better lighting, and to remove added strain on the headlight switch. ( at this point I will still be using the sealed beam headlight/ but at some point may upgrade to better bulbs. On chrysler cars the power goes from the battery/ to the starter/ then to the starter relay on the firewall. Must of the power is run off of the starter relay. I was planning to run the alternatog 8ga wire to the battery lead one the starter relay..
The extra amps coming out of that alternator are not going to affect your stock wiring unless you have Items that draw amps in excess to what the system draws now as Steve tried to explain. As he said, I wouldn't get carried away with putting an off the wall fuse block setup on it. I've got a big frame Delco 80 or 100 amp alternator on my 77 1 ton with a 454 with no accessories and oem style halogen lights. 4 speed bare bones work truck but I need the amps when I am running my hoist for the 10 ft flatbed. That is the only time there is more than a 15 or 20 amp draw or alternator output on that truck. Most of the time it just puts out enough amps to charge the battery after starting and then make up for what little draw the truck has.
What precisely do you feel that needs additional protection? The aftermarket has convinced too many people that these fuses are needed, when in reality it's just a way to separate you from some additional money. Remember, fuses or other overcurrent devices are there to protect the wire, not the device. They offer two forms of protection; overload and short circuit. There's four ways of dealing with this; fuses, slo-blow fuses, fusible links and circuit breakers in order of fast to slow how fast they'll clear an issue, pick one. I'll assume you're worried about the alternator wire and the feeder to the fuse panel, so let's look at those. I'll start with the alternator. You're upgrading to a #8 and that's good. That size is rated for 45 amps, but because the alternator is capable of putting out nearly 80 amps, that's the minimum fuse size you'll need. First problem, you've fused the wire at 180% of its rating. So no overload protection there. Second, to fully protect the wire you need a fuse at each end because 12V power is present at both ends. That's eight additional failure points, figuring four wire connections and two connections for each fuse. I'll also note that alternators cannot produce more than their rated current output and when they do fail, they fail to 'open' (no power outputted). The feed wire to the fuse panel. The factory has calculated how big this wire has to be (although they've made it as small as possible). There are no loads directly connected to it, and all branch circuit loads have their own individual fuses. As long as the OEM wiring hasn't been altered or too-large fuses used, the feeder will never see a killing overload. To calculate the required fuse size, add up the fuse values. As #12 wire is only rated for 20 amps, anything over that will limit your overload protection. That leaves short circuit protection. What was done when that car was new was simply to route the wires in such a way to give them as much protection from physical damage as possible. Stay away from sharp edges, don't let them flop around and rub on stuff, and keep them away from heat sources. This the one place the fuses may help, but only under certain circumstances. In the event of a serious collision, collapsing the engine compartment, these wires may be damaged although personally I'd be more worried about the battery. If the fuse is grossly oversized (150% or more), it will take a solid grounding to trip the fuses. What's more likely is they will simply arc, burning individual strands until the wire parts. This isn't my first post on this. In an earlier one, one poster noted that he talked to one of the major aftermarket vendors about this a number of years ago. The tech told him basically what I'm saying; they're a waste of time. That vendor is now selling these, figuring that if they didn't offer them, the customer might go elsewhere. They climbed onto the bandwagon.
I had a similar discussion with American Autowire one year at NSRA Louisville. The conclusion was that protection was not needed. Thanks @Crazy Steve .
That's why I talked to them, but I questioned what they really protect and the end result was, "very little".
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