As I plan out the wiring for my flathead powered 30 coupe, I'm wondering which circuits are you guys running fuses on. I'm using a 12v generator and minimal electrics (no radio) Thanks, Carl
Well I probably run different ignition that you do so this probably don't count but I used an inline fuse on the line in for my distributer. It is a good idea to fuse anything with a switch. Lights, ignition, fuel pump. You should not have much more than that.
Depends on the car. My old truck (59 Chevy) has reproduction original wiring, which does not have any fuses except for the dash lights. There are two circuit breakers on the original light switch, one for headlights, the other for the rest of the lights. It also has the original dealer type accessory fuse panel for the radio, heater, etc. I think I added a #14 fuse link to the wire that goes from the starter battery terminal, to the main feed to the rest of the harness. On my Chevy II, which has a mostly home made harness, there are fuses for the unswitched and switched circuits, but not for the headlights. Keep in mind that the fuses are there to protect the wires. That's all. If a wire or what it's connected to gets a short to ground, the wire will carry a LOT of current, and get hot very quickly. But if there's a fuse in the circuit between the power source (battery or generator) and the short, then the fuse will blow and prevent the wire from overheating. So...think about where there could be issues with wires getting shorted to ground, or devices failing in a way that causes too much current to flow. If you have a generator and mechanical voltage regulator, a known failure point is the cut out relay sticking, so the battery is connected to the generator windings after you shut off the engine. A fuse in this wire can prevent catastrophe. It's a good idea to size the fuses to match the wire size. Typical sizes are 30 amp for #10 wire, 20 amp for #12, 15 amp for #14, etc.
I use circuit breakers - one 50 amp in the charging system, & one 30 amp for the accessories. If it has a tube radio, I fuse it.
I'm putting a new wiring harness in my '50 truck because I'm not smart enough to answer your question even for myself. I do notice that there is a fuse for every circuit, though. But my suggestion is, just be sure you can easily add a circuit later if you chose to, like if you want to add fog lights for example. It's better to have a fuse or two standing by, available than to have to add another board. In my truck, the original cigarette lighter is long gone, but I'm adding one back as a power port. It won't have the old coiled metal deal to heat up and pop out because I'm not a smoker. I'll have a plug w/knob in there when I'm not powering anything.
All helpful and this is worth the price off admission! Thanks Jim. Below is my schematic so far - it's a WiP. Comments welcome. Thanks, Carl
The more you like the car, the more of the electrical system you protect with fuses. The starter usually don't have one, maybe not the generator/alternator, but anything else should absolutely be protected. A shame to burn up the car just to save a few minutes and dollars not adding the fuse that would have stopped the fire.
This is very basic info that I'm sure you already know......... But the fuses should be upstream, before the switch, not after. I've seen folks mistakenly do the opposite, usually when adding an accessory "kit" that comes with one of those fuse holders already spliced in the wire. I'm not a fan of those cheesy, inline fuse holders, by the way. It's too easy to forget where they're at and because they look like dooky, a lot of people cover or hide them so you would need a treasure map to ever find them again.
Since you are using a 50s style headlight switch, I would try to mimic a schematic from the car that originally used that switch. It's kinda hard to follow the schematic, especially as it relates to the generator and battery, but that should be fused and possibly to the starter. Typically, wires to the starter are not fused because of the amp draw, but with today products, it isn't an issue, and I would definitely fuse that wire because lots of fires start with starter issues. I could see the horn on a separate circuit, ignition on another, headlights on one, driving lights on one, interior lights on one, and brake lights/dash lights on another. I didn't see a radio or other accessories, but if you have a heater motor, I would put that on separate circuit.
Yes, I have been pretty faithful to the 1950's schematic, but unless I'm missing something they only have three. On on the headlight switch, one for the turn signals and one for the heater. And yes, I do plan to add those to my schematic. I was just curios if I should add more. Very helpful responses so far. Thanks, Carl
You can definitely combine circuits on the same fuse. It usually comes down to cost in original designs. My wife's Acura RDX stopped working a few weeks back. She called me and said the dash was all "lit" up with warning lights, and she couldn't shift it out of park. After getting it out of park using the manual shift lock, she went directly to the Acura dealer. They diagnosed the problem as a blown horn fuse. The issue was that the rear brake lights were on the same fuse. The computer detected that there were no brakes lights, so it disabled the shifter for safety reasons. Lol...
Original manufacturers only added the minimal amount of fuses because of cost. Anything that has electrons flowing through it should be fused, or at least have a minimum risk of a short to ground ,E.G. a starter circuit could be fused, but 400-800 amp circuit breakers would be huge and expensive. When I wire a car, I always leave 3 or 4 extra positions in the fuse panel, which can be used later. Keep the unfused (the supply to the fuse block) wiring safely insulated (double thickness insulation, grommets, etc, ) and as short as practical. The fuses will handle the rest. Don't go putting 35A fuses in a 1 amp circuit, (as I have seen many times) rate the fuse for that circuit correctly.
Be careful of the fuses themselves - on another electronics board I frequent somebody actually tested the el-cheapo-from-you-know-where fuses and discovered they weren't even close. Fortunately there are still plenty of good ole N.O.S. Buss and Littlefuse to be had.
Not sure where you are getting 800A for starter current. Yes, there is always an in-rush current for motors, but fuses and circuit breakers are usually designed with a built-in delay protection. I can see several hundred amps continuous for a starter, and LittleFuse has their line of MegaFuse products. https://m.littelfuse.com/~/media/au...bolt-down-fuses/littelfuse_mega_datasheet.pdf
I use circuit breakers in almost all circuits I build. The reason is if it just a spike or temporary short the circuit will come back on. That’s why you rarely see fuses in headlight circuits. Just me, not that much more in cost. Bones
So Bones, you're saying at the very least you would use a circuit breaker for the headlights? And Ziggster, you're saying to fuse the whole system at the starter?
As far as I know, most automobiles use fuses. The reason is cost and purpose. Fuses have been used successfully used for 70 plus years. I used Eaton circuit breakers in our bus HVAC systems for several reasons, along with regular automotive fuses. Bus manufacturers would specify circuit breakers usually for larger HVAC motors. This was for ease of troubleshooting/repair, but also for protection purposes as fuses usually took longer to blow, which potentially was enough time to have a fire start. In the military Light Armoured Vehicle (LAV/Stryker) we used circuit breakers exclusively. Again, primarily for troubleshooting/repair and safety reasons. I have a 9000 lb SuperWinch on my truck, and it is fused with a 250A mega fuse. It is rated at 4.6 Hp which works out to 254A at 13.5A and I have never had the fuse blow, even under some long and heavy pulls. Yes, I would add a fuse on the wire going to the starter.
Here's what I did FUSES gauges Dash lamps Brake lights Parking lights Hazard flasher Turn flasher Dome light and cigarette lighter Wipers Horn Radio heater/AC (Fan) CIRCUIT BREAKER Headlights FUSIBLE LINKS Fan Stereo amp & power antenna Ignition switch (B term) Notes: 1. Power to operate fan relay has fuse. Power to fan that is switched by relay is protected by fusible link. 2. Inputs to fuse block terminals I, B, and A are from ignition switch terminals I, B, and A
If you look at tri-5 Chevy's the schematic is similar to yours. [attached] On mine we added a fusible link in the main power feed off the starter solenoid. A 57 Chevy runs a "total loss" fuse system from the battery to the ignition coil [only accessories are fused] When an electric wiper is optioned, it takes it's feed from the ballast. If the wiper jams it melts the main ignition wires. If I was doing your car from scratch, I would add a Ford style solenoid near the battery [and take the main power feed from there] ,and the solenoid on the starter motor gets bridged. Doing it this method leaves all the H/D battery cables dead as a dodo until you start the engine.
Very helpful info all! So a few more questions. A fuse or fuse-able link from the starter solenoid to the main harness? This would isolate the whole system if open and should protect from Jim's scenario (I think). What size fuse/fuse-able link for this circuit? Expected electrical items used. headlights parking/turn/brake lights electric fuel pump computer fan for heater (1amp) gauge lights (4 incandescent) turn signal & high beam indicator lamp ignition circuit windshield wiper motor IF i can't work out a vacuum source for the stock motor.
I have not recently installed fuses on any circuit I have made. By the time you buy a fuse block and a box of fuses ,you can almost pay for a circuit breaker. The neat thing about circuit breakers is that they will reset and if the short or overload has been eliminated, either temporarily or fixed permanently, returning power to the circuit. OEMs thought the headlight circuit was important enough to do this , but not any other! I think all circuits are important or I would put them in! Just me. Bones
You size the fuse for the wire it is feeding, as it is the wiring you are protecting from overload. If you put a big fuse before a heavy wire straight from the battery (for example) to protect the heavy wire, you then put multiple smaller fuses where it is split up into many smaller wires feeding a number of different systems. That split would normally be a fuse box . One heavy wire to it to feed it, many smaller going out.
Understood. My question above however is about the master fuse-able link for the whole car. Thanks, Carl
Generally the main H/D cable from the battery to the starter is not fused. On your schematic a fusible link would be on the yellow wire from the starter relay [solenoid] On touring cars [road racing] it is normal to put the battery in the trunk. So for safety they put a Ford solenoid [starter relay] right next to the battery and then bridge the other solenoid on the starter motor. The yellow wire power feed and starter switch wire [on your schematic] will go off the Ford Solenoid. This method keeps the H/D cables dead [after the Ford Solenoid] except when the starter switch is activated. If you want to put in a battery disconnect! All you need is an inline switch on the same yellow wire. Attached is a schematic of the Ford solenoid in a GM car. [for safety you want Battery to"A" to be short as possible] The main fused power feed [yellow] would come off "A" If you think about it...........Your schematic with a "starter relay" is already like this! Just mount the relay close to the battery. And if you use a solenoid type starter it needs to be bridged
Mimilan, thank you for taking the time to review my schematic, I appreciate it! And I appreciate your write-up below. I've been updating my diagram to include fuses (or circuit breakers) and relays. I will post when complete - I hope you can look it over with a critical eye. One question, on you diagram below, is the (I) post capable of handling the load of the rest of the car? Thanks, Carl
Learn to do a bit of math here. 1 amp x 1 volt = 1 watt [2 amp x 12 volts = 24 watts] So if you are using 2 x 65 watt headlights it would be 130 watts 130 watts ÷ 12 volts = 10.83 amps [a 15 amp fuse is enough] On the headlight circuit you need to add up the total watts of the headlights [high beam] Taillights and instrument lights to figure maximum draw. In our country we can purchase wire by an amp rating [which is simple] but in the USA you buy it by gauge ,so a conversion chart is needed.
I wire my own cars and I start every job by installing a 150 amp circuit breaker on the cable between the battery and 4 pole kill switch (not a disconnect switch). The kill switch routes alternator power and accessory/fuse box/ignition power. The only thing not ran through the breaker is the starter power that is ran through a ford style solenoid. The way I wire is not cheap but then again I spend a lot of money on my builds, this is fire insurance of a sort.
I just used a simple 12 circuit eBay wiring set up. Followed the instructions and everything worked. Replaced the cheap ignition switch after year. Best 150 bucks I ever spent on a build.
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