Electric fuel pump in a 12 volt '49 F-1.

I would like to run the fuel pump on a relay through the starter button so that the fuel pump does not start running until the starter button is pressed (not when the key is switched on).

That's easy enough, but obviously the relay needs to remain energized after the starter button is released and shut off when the key is switched off.

Thanks

 

That's a latching relay. They're not cheap.

 

Like this? Sounds right by the description

785XBXCD-12D - Magnecraft / Schneider Electric - Latching Relay, DPDT, 16A, 12 VDC, 10 Pin Blade; Solder

I can live with the price, it just better come with a good wiring diagram.

 

I don't think that will do it. Look at the application notes: http://www.galco.com/techdoc/mgcr/785xbxcd-12d_app.pdf

See the sentence under Magnetic Latching Relays; "Magnetic latching relays are useful in applications where interruption of power will not transition the position of the contacts." So if you turn off the truck, the relay won't open the contacts. Mechanical Latching relay doesn't seem to work either, for what you want to do.

You may be able to use a regular relay by adding some external components. Why don't you want to run the pump until you start the engine? Usually you want to build pressure/flow first. Also, consider using one of these: http://www.holley.com/12-810.asp

 

My first question would be why . Whats wrong with connecting it to the run position on ignition switch through a simple SPST relay ?

 

Don't want the pump running if the key is turned on.

 

Does your ignition switch not have an accessory position ?

 

It would be simple to put a switch in the feed to the pump if you don't want it running.

 

It does and I might still go that route. Actually I probably will for the time being and see how it works out.

 

I have my electric fuel pump connected from the "S" terminal of my starter solenoid, only gets power when the button is pushed, then I have an oil pressure switch that picks up power when the engine is running, seems to work good. Now I do have a redundant solenoid as I have a high torque starter with a built in solenoid and I still chose to put one on the firewall for the original look and accessory wiring.

 

I'm still puzzled why you would want the key in the Run position but not have power to the pump? If you want to listen to the radio, the Acc position is the one to use. In Run, you also have the ignition system energized.

It would help to know whether this truck has a stock engine/ignition/etc or is a fuel injected SBC or whatever.

 

Gave that some thought, the first reason I came up with was if there is any damage in the fuel system I didn't want it leaking all over if the key is on.

But the real reason is it's just the sort of gadget I like building. It's entirely for my own amusement.

I rewired it so the pump doesn't run in accessory position, I'll probably leave it at that for now.

Thank you for all the input.

 

The pump should absolutely be on the IGN side of the switch. I think what you really want is the Holley safety shut off switch. If the engine dies for whatever reason (accidents in particular, but also a ruptured fuel line), oil pressure dies and the switch kills power to the pump. The switch is bypassed while cranking, if you hook it up right. OEM's use a similar setup, sometimes in the engine computer, looking at ignition pulses.

 

The start button on the 48-50 Fords are ground connection - It's not a hot wire

 

If you still want to do it, I can tell you how, but not using a standard Bosch or Tyco automotive relay (which is a single pole). You would need a double pole 12vdc relay and a diode to pull it off. It would start pumping when you hit the start button, and continue pumping until you shut the ignition off. I agree with the above poster, though - I would use an oil pressure based system, that way in the event of an accident or engine problems, the fuel pump is turned off. The only problem with that is that it will still run until the carb runs out of gas.