12v ignition switch source

[martingmc86]

I need help finding a firm 12V ignition switch source to to connect my electrical fuel pump and my atomic msd efi does someone know where I can get a good connection from and please point it out

 

[Ricko1966]

I need help finding a firm 12V ignition switch source to to connect my electrical fuel pump and my atomic msd efi does someone know where I can get a good connection from and please point it out

How I'd do it. A typical parts store four prong relay. Terminal 30 to battery, terminal 87 to fuel pump,terminal 85 to alternator exciter(light) wire, terminal 86 to ground .
THIS WAY THE FUEL PUMP ONLY RUNS WHEN THE ENGINE IS RUNNING!
If you need fuel pump to run while cranking,you can run a wire from the starter solenoid through a diode to terminal 87. If you simply just want to grab a 12v source that's only on with ignition on,you can grab it at the wiper motor.

 

[Grit dog]

Mine (86 with a newer engine and electric fuel pump) was run from the electric choke wire…eek when I bought it.)
I kept the choke wire as the trigger for a relay. However you don’t want just a simple relay (long term anyway) as that will put power to the fuel pump 100% of the time when the key is on.
There is a timed relay you can buy for powering fuel pumps that works like newer cars do. Dozen different reasons why powering the fuel pump contiuously is a bad idea as an even semi permanent solution.

 

[gmbellew]

Mine (86 with a newer engine and electric fuel pump) was run from the electric choke wire…eek when I bought it.)
I kept the choke wire as the trigger for a relay. However you don’t want just a simple relay (long term anyway) as that will put power to the fuel pump 100% of the time when the key is on.
There is a timed relay you can buy for powering fuel pumps that works like newer cars do. Dozen different reasons why powering the fuel pump contiuously is a bad idea as an even semi permanent solution.

I am curious about this. Pretty sure my TBI has 12v to fuel pump always when the engine is running. Is that an issue?

 

[Matt69olds]

Use this:

Fuel Pump Safety Switch

Shuts off the fuel pump if the engine stalls. Primes the pump at startup.

www.revolutionelectronics.com

Wiring a pump to run anytime the ignition is on isn’t a good idea. Yes, people do it all the time, but it not smart. What happens if someone plows into you and you’re unable to reach the ignition, or worse unconscious while the fuel pump is feeding the fire underhood?


Another option:

https://www.motortrend.com/how-to/safe-and-efficient-electric-fuel-pump-wiring/

This uses a Vega oil pressure switch to control the pump. The engine loses oil pressure, the fuel pump shuts off.

Either way, if the pump draws more than a few amps, wire it thru a relay. Take it one step further and wire a hidden switch to interrupt the trigger. Built in cheap anti theft device!!

 

[Grit dog]

I am curious about this. Pretty sure my TBI has 12v to fuel pump always when the engine is running. Is that an issue?

Yes when the engine is running. No when the key is on but engine not running.
The relay I mentioned you don’t need. Your car already has that safety feature if you will.
But for vehicles that don’t have efi supporting electronics…
It primes the system for a couple seconds when the key is turned on like most modern efi vehicles then turns off and there is a tach signal wire that starts the pump again once it sees x amount of rpm’s. I think it’s more than cranking rpm’s and less than idle speed.

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[Grit dog]

Use this:

Fuel Pump Safety Switch

Shuts off the fuel pump if the engine stalls. Primes the pump at startup.

www.revolutionelectronics.com

Wiring a pump to run anytime the ignition is on isn’t a good idea. Yes, people do it all the time, but it not smart. What happens if someone plows into you and you’re unable to reach the ignition, or worse unconscious while the fuel pump is feeding the fire underhood?


Another option:

https://www.motortrend.com/how-to/safe-and-efficient-electric-fuel-pump-wiring/

This uses a Vega oil pressure switch to control the pump. The engine loses oil pressure, the fuel pump shuts off.

Either way, if the pump draws more than a few amps, wire it thru a relay. Take it one step further and wire a hidden switch to interrupt the trigger. Built in cheap anti theft device!!

Yup on all accounts.
My truck will start and run for about 30sec with the hidden switch off. Then it dies. Suddenly It aint got no gas in it!

 

[Ricko1966]

The circuit I posted earlier,does almost exactly this for about 10.00

Fuel Pump Safety Switch

Shuts off the fuel pump if the engine stalls. Primes the pump at startup.

www.revolutionelectronics.com

The wire and diode turn the pump on while cranking to start the vehicle. The relay uses the alternator as signal, instead of using tach for signal. If you need your three second prime forget the solenoid wire and diode, run a momentary contact switch to 87 push to prime,if you need prime,there's your anti theft also, unless the thief knows to push the momentary contact switch. Just to clarify if the alternator isn't spinning,the relay won't close.