Electrical wiring (fuel pump with relay and toggle)

I'm wiring my 1940 merc that's converted to 12v -ground using stock style replacement harness. I'm wiring up my 12v carter fuel pump and using a relay connected to a toggle switch on dash.

Do you know where I can find a diagram? Or is the attached diagram that i made correct. I don't know If I run + from battery to fuse block then relay OR batt + to relay and fuse block to one of the terminals on toggle switch?



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This is how it should look I also would use a inertia switch from a Ford, wire it in either side of your switch. Just in case you get in a wreck the inertia switch shuts the fuel pump off. I prefer this than a oil pressure switch to shut off the pump it makes dry bowl start ups a lot easier. You do need to fuse the switch as well. It is a good rule to fuse all positive leads as close to the source as possible.

 

But where is the fuse block and switch in the diagram?


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Your diagram will work fine, just be sure the switch fuse is only powered when the key is on ignition only. Amx180mph's diagram looks like one for adding a relay where the pump was only controlled by the switch before. If you add the fuse and switch to the wire at the top of his relay it's the same as yours.
I have installed them with the Ford switch mentioned and/or an oil pressure switch, it just adds a little safety factor.

 

See the HUGE 2 prong fuse, upper left. Wired between battery and relay.

Switch is not shown, but it is where the top left says: Red fuel pump power wire.

 

The fuse is the thing in the upper left corner of the drawing. Just above it is the wire that goes to the switch.

 

I'm thinking it makes sense to wire + from battery directly to fuse block where other accessories can be added later.
If this diagram is ok as described + to 8 circuit fuse block... there are two terminals on toggle switch. Where does the remaining terminal go?


And would each accessory it's own relay?
This diagram is what I'm thinking.


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The switch would go inline between the fuel pump power wire and fuse block. As 24riverview suggested that it needs to go to a circuit that powers off with the key.

 

This shows a dash mounted switch just replace the Holley oil pressure switch with the fuse block pick a circuit hot with key on.

 

an inertia switch or oil pressure switch is a must have,dont run it without.or should i say dont drive it without some sort of safety feature.

 

Each load should have it's own fuse and relay. In your drawing, you have a couple of choices... You can jump pole 30 and 86 together and run the wire from from pole 85 to the toggle switch and a wire from the other side of the toggle switch to ground. This is how the factory switches devices like the fuel pump.

More typical for DIYers would be to ground pole 85, and run another 12V+ lead to the other pole of the toggle switch. Either way will work.,

 

I energize the pump with an oil pressure switch that closes at 10 psi. I have a momentary contact toggle wired in parallel with the oil pressure switch so I can hold it on if I need to and an indicator light to tell me when there is power to the pump. I've seen too many relays stick on when the contacts weld together. Late 80s and 90s Ford fuel pump relays seemed prone to failing on. If the battery goes dead in a few days of sitting, it is likely the fuel pump is running.

You do need an oil pressure or inertia switch or both wired into the system to shut the pump off in case of an accident or broken fuel line. The inertia switch can't tell if the engine isn't running so it would allow fuel to pump with a broken line if you don't turn the switch or key off.

When Florida had rental car license plates, thieves would target Ford rental vehicles. They would bump into them from behind which tripped the inertia switch. Then they robbed the stranded tourists.

 

I've never liked to use the ground side to control a relay because it's too easy to get an accidental ground in a circuit. If a switch fails it can ground or a wire can chafe and ground. That being said, many factory computer systems control the ground on a relay.

 

Agreed, I burned all the hair off my face working on a propane system for that very reason. Just wanted to point out that electrically it could be done both ways (saves wire length, too).

Also agree on the oil pressure switch. I wouldn't run an inertia switch on a hot rod if somebody had a gun to my head...

 

As another alternative, Ron Francis makes a fuel pump wiring kit that includes a relay and a collision shut-off safety switch. I wired one into my truck and am pleased with the ease of installation and having the extra safety feature.

 

Ok. Final draft here. Based on the responses I got from you ol' timers I have:
1) removed the toggle from the diagram allowing my ignition switch to trigger the relay.

2) sounds like an oil pressure switch is the best type of safety. Where in my diagram in this post should I put the pressure switch?

3) do I really need to worry about the relay sticking in the on position, not allowing my ignition switch to shut off fuel pump.


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Link still not flying...

 

sorry having a bit of trouble loading the pic. Try in a bit

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Not sure what the "gauge" post is on the Ignition switch...just make sure it's hot in run (I'm guessing it is). The rest of it looks fine.

 

Check that gauge terminal, it's most likely hot in run position but not in start. If that's the case, move that wire to the ignition terminal. Yes, most carbureted engines will start if there is fuel in the bowl, but if not, you'll kill the battery long before fuel gets there.

 

Hi .... You could also use a pulse trigger switch for safety... to switch the fuel pump off in case of a crash .They are about $28.00 here in Australia.....It works from the pulse side of the coil or the tach output on dissy...when ign is switched on gives a 5 second pulse to get some fuel to carb and then dosent work till the dissy is turning around..I aways use them with electric fuel pump for safety......Doug

 

When did electric fuel pumps start to pull so many amps that they suddenly need a relay? Is this an internet phenomenon? I've had an ass load of electric fuel pumps on 40s and 50s style hotrods (which sounds like what he was talking about) and never once used a relay. I'm talking about carbureted cars and not the fuel injected modern POSs

SWs Dupree's, ACs....none of them ever required a relay. A fuse yes but never a relay. What happened in the 80s-90s and 2000s that makes a relay necessary? What did I miss. Was there an epidemic of burned up hotrods that didn't use a relay? A relay to me is just something else that can and will fail on the road. If it's not necessary...I don't want one on my hotrod.

I believe in the KISS system...Keep it simple stupid.

Just another unpopular opinion I guess. I've got a lot of them.

 

Tommy,I think the relay crap started when the auto maker brainiacs started putting the fuel pumps in the gas tanks. Then they thought why not make some more crap to screw up and put 2 fuel pumps on vehicles ,a low pressure in the tank,then a high pressure in the line. I am with you ,fuse,switch,good ground and drive.

 

It's not always about AMPS, sometimes it's about CONTROL.
If you put a new switch on the dash each time you added something electrical, you could end up with a not so simple dash. Then each time you start the car, you need to flip a bunch of switches, then remember to flip them all off when you park.
Using a relay on the existing (60 year old) ignition switch will allow it to turn on an unlimited number of devices simply by turning the key. Then you can add safety devices like an oil pressure switch that may not have the current rating to run the pump. Sometimes being too simple is kinda stupid.
Besides, the OP wanted to learn how to wire a relay. He didn't ask if it was really needed.

 

I agree I'd shit can the toggle switch too. When I was a kid I wanted a toggle switch to show off the fact that I had an electric fuel pump. Flip the switch and hear the pump click away. It didn't take long for me to figure out that a separate switch was a PITA.

I just run it to the "run" terminal on the ignition switch. That 60 year old switch was engineered to carry twice as much amperage for the old 6V system than a modern 12V system uses and I've always used them with no problems. I do check them out before hand though.

Remember I'm are talking about old time hotrods and not modern streetrods with all those bells and whistles.

 

Tommy,
No argument about your points. I just like relays because they let me use itty-bitty wires and tiny (hidden?) switches, and keep the high current wiring out from under the dash and shorter.

 

I must admit I have never checked the current rating on an electric fuel pump but IMHO it's nothing to be concerned about. I do use an inline fuse like the ones on the radios before they became standard equipment. That's probably before your time. I'm an old fart.

I personally like the old looking switches, original ign switches and starter buttons etc. In fact I once wired a horn relay into the start circuit of a SBC just so that I could use an early Ford starter button on the dash simply for looks. It was overkill but the look was important to me. I could have used a generic starter button but I wanted that old Ford look.

 

You mean these fire hazards?

Had one of these damned things fall apart under the dash of a 66 Coronet once. Unfortunately it was running the lights, and the short end fell down on the dash lip. POOF! So the only light I had was the insulation flaming up under the dash...

I like older switches for looks too. I'll just hide the modern stuff away where no one sees it.