Hey everyone. I want to get your opinion on some wiring schemes. So I need to be able to power my pertronix ignition and electronic fuel pump. I was thinking to do this I have 4 ways 1. Wire goes from battery to 20 amp toggle switch, toggle switch powers relay which then goes to fuse block then to ignition and fuel pump (probably safest way to do it) 2. Wire goes from battery to big 50 amp toggle switch ten directly from switch to ignition and fuel pump 3. Wire goes from “on” post on ignition switch to relay then from relay directly to fuel pump and ignition (might add fuse block you all think it necessary) 4. Wire from battery to 50 amp toggle switch then to fuse block then to fuel pump and ignition. Now for all these with a relay I was thinking using a 40 amp relay maybe 30 amp but I’d rather go higher than necessary just for peace of mind. Also I don’t know which terminal is the “on” post on the ignition switch also I don’t pull to much voltage through the switch (although it’s only powering a 40 amp relay). I like option 2 because it’s easiest but it’s also least safe if something shorts out. Options 1 and 2 also have added benefit of being anti theft because you have to flick switch for vehicle to run
One of the cool things about using relays in circuits is there's no need to pass high amperage through ANY switch. Main power goes straight to the relay and you can control the circuit through the relay by either applying a low amperage + to the relay to actuate it (switched), or grounding the relay to actuate it (unswitched).
You need to run a fuse no matter which method you use to help prevent a wire burning up, short, and electrical fire. Also; there should be exact fuse amperage recommendations for both of those items. I think fuel pumps are only 5 amps? I'm not too sure. I don't know what the amperage would be on the pertronix ignition either. Maybe 10? It depends on what electrical you have in the car, but I would wire like so: 12V coming from battery with 3AMP fuse connected into BAT terminal of ignition switch. 12V coming from battery with 5AMP fuse connecting into a relay. The "trigger" lead from the relay would wire into the "IGN" terminal of ignition switch. The "power" lead from the relay would run to the fuel pump itself. 12V coming from battery with 10AMP (maybe? I'm not sure what the amperage is on a pertronix ignition?) fuse connected into a relay. The "trigger" lead from the relay would wire into the "IGN" terminal of the ignition switch. The "power" lead would run to the pertronix ignition. Doing it this way insures each 12V is fused properly. Using relays and trigger wires means that no electrical stress is placed on the ignition switch itself. When the ignition switch is turned to "on" the pertronix and fuel pump will be energized through the relays. Standard 30/40 AMP relays will work with this. When you have exact amperage measurements you can also figure out wire sizes needed.
Find Crazy Steve's story about Wiring 101 and when you get totally confused....keep in mind that you just need to power a couple things that don't really have high current demands. The ignition system doesn't take much current, and the car should already be wired for it, eh? just connect the Pertronix to the coil wires. The fuel pump might be a bit more involved, if you want it to shut off when the engine stops running. Depending on which pump you use, it should draw less than 5 amps, so you don't really need to get very fancy with wiring it. But adding an oil pressure switch to shut it off might be a good idea. Using a mechanical pump like original, instead of an electric pump, might be an even better idea. What condition is the original wiring in?
On the 40's we do with stock ign switch the batt feed (hot all the time) to panel has a maxi fuse. The acc side is powered by a relay. Only minimal current thru ign switch to energize relay for acc side of fuse box. Then coil energizes from acc side of panel with switch on. Elec fuel pump is fed by a switch in the wire from the acc side of the panel to energize a relay for pump-elec pump is only an auxillary pump-thus the switch-main pump is stock..
The wiring is kinda a kind of a mixed bag. Before I got to it it had been sitting in a field and the mice got it first. It looks like all the radio wiring was chewed up but all the instrumentation and ignition and lighting wires are ok. The only reason I didn’t use the stock ignition wire is because it’s a resistor wore and only has about 6 volts by the time it hits the coil and the pertronix units call for 12. Reason for running electric pump is to avoid vapor locks forming in 90+ degree temps
1 or 3 would be fine so long as you place appropriate fuses. Pertronix doesn't haul really any amperage to be worried about, and unless you have a super fancy high volume fuel pump, it won't typically haul more than 10 amps. I would caution that the pertronix should be wired in parallel with the coil, such that the 2 components have their own power feed. Pertronix units are super picky I've found. Unless you have a need for toggles, I'd just run it off the ignition switch. Sent from a Glade Air Freshener.
Relays have their place, usually in moderate to high amp draws, and are used to shorten the heavy wiring and allow use of smaller switches. But any time you add components, you add possible trouble points, that is more connections etc. Either way will work, use the one you like, but always place a fuse as close to the power source as possible. Usually the fuse for the appliance will be too large for the signal switch, necessitating two fuses...... more components.....more connections...... get my drift. Bones
I get it. Can I just do this 4 GA wire going to 50 amp switch from switch to fuse block then to ignition and fuel pump separately. No need to complicate it with a relay. Or I can just put the ignition through the stock 6 volt resistor wire and only have the fuel pump run through fuse
Maybe I misunderstood your project???About the only place a 4 Gauge wire would be used , would be something close to a starter! Might want to check your amp draw on your peticular appliance and select the appropriate gauge wire. I almost always jump a gauge higher, actually lower, ( bigger that is) , but 4 gauge wire is huge! Edit: most complete electrical systems on most 50s/60s cars were fed with about a ten gauge wire. Bones
Relays are very simplistic, I wouldn’t view them as complicated in any means. You can get 5 of them for a few dollars, and keep them in the car if you’re worried about it. As stated before 4GA wire is massive and way overkill. The max you’re pulling with both of these electronics is only 15 amps. A 14 GA wire would even be on the safe side.
X3 on crazy steve's wiring 101......wire size is for the load that is needed and fuses are to protect the wire! Search and read the wiring 101 thread, you are way overboard on what you're talking about for wiring!
With everything you wire except for the starter, it goes battery, fuse, switch, powered item, ground. Repeat.
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