[riesman20]

Can anyone tell me how to tie in and electric fuel pump onto my 1984 GMC truck with a 305. I am speaking electrically of course. I am guessing that it should not turn on with the key but when the motor is turning. Also what pump is best?

[Siggy_Freud]

If you are going from a mechanical to an electric you will want to wire it in so it turns on with the key on. If you wire it for when its cranking it will shutoff as soon as your done cranking. The key on position is the position that the key is in when you drive so its where you want it to be wired. As far as what is the best? Depends on what your going for. As a stock replacement I'd hitup autozone or napa (or your local autoplace) and pickup their universal pump that pumps 5-9 pounds of pressure.

[Pony]

Chack your otherpost. it has more answers.

[willys36@aol.com]

Electric pumps should be on when the key is on. I wire mine through an oil pressure switch too. Get a pressure switch (I think 7psi is what I use) from the auto parts store and install it in the pressure gauge port of the oil system. Wire the pump from the crank terminal on the ignition switch so it will pump when cranking. Then wire from the "run" ignition switch terminal through the pressure switch so if the engine stops so does the pump.

[Tech @ BG]

Wiring an electric fuel pump for a street driven car:

Run a wire from a "keyed on" (only hot when the ignition is on) source to an oil pressure safety switch (hobbs switch). From the pressure switch run a wire to a 30 AMP relay. Ground the Relay to a good chassis ground. Run a wire directly from the battery to your relay. Now run a wire from the relay to the fuel pump, and ground your fuel pump. Run a 25amp fuse from the battery to the relay, and a 5amp fuse from the switched wire to the pressure switch.

When you turn the key "on" power will go to the pressure switch, once you crank the engine over, and it get oil pressure this will complete this circuit. This will turn the relay on, feeding power to the pump. Wiring this way will make sure you get full voltage to the fuel pump, but that it will only stay on when the engine is running, or has oil pressure.

[riesman20]

Is there a difference betweeb the existing oil pressure switch and the safety switch? Or will any oil pressure switch do the same thing?

[willys36@aol.com]

Look at the circuit diagram in this thread;

Holley safety pressure switch.

[dmorris1200]

I like the schematic in the Holley link but I would still hook the output of their switch to a relay like Tech @ BG stated so that the solenoid/pressure switch turn on a relay and then the relay kicks on the pump. If you ever need to crank over the engine for any reason without it starting (compression tests, etc.) you could simply unplug the relay preventing the fuel pump from turning on while working on the engine. This comes in handy often on late model cars where the fuel pump relay is generally located in the engine compartment.

[riesman20]

Ok, I purchased the required equipment. The electric pump states that it should be mounted near the tank but I want to mount it under the hood will that be a problem? Does anyone know where I can find an ignition diagram on line?

[dmorris1200]

Electric pumps are better 'pushers' and should be mounted as close to the tank as possible.

[willys36@aol.com]

Originally posted by dmorris1200
I like the schematic in the Holley link but I would still hook the output of their switch to a relay like Tech @ BG stated so that the solenoid/pressure switch turn on a relay and then the relay kicks on the pump. If you ever need to crank over the engine for any reason without it starting (compression tests, etc.) you could simply unplug the relay preventing the fuel pump from turning on while working on the engine. This comes in handy often on late model cars where the fuel pump relay is generally located in the engine compartment.

Good point d. Get in the habbit of installing relays between motors and switches everywhere on your car. Switches are often crappily made, aree high maintenance and cost as much as a motor. Better to have a relay do the heavy lifting and let the switch do light duty of signaling the relay.

[Tech @ BG]

The main purpose of the Relay is to make sure the electrical item (pump in this case) gets full voltage from the battery. All DC motors are voltage sensitive, and the further the voltage has to travel through the wiring the more resisitance there is (giving you less voltage).

[riesman20]

I have 3 last questions gentleman. 1. the 30 amp relay I purchased has 4 points on it I believe they are 30, 85, and two 87's . How do I wire it in correctly?. 2. I purchased a safety switch that is NC at 11 psi and NO at 4 psi this should be good correct? and 3. Pardon the ignorance, but where is the best place to tie into the ignition system? Thanks.

[riesman20]

This is what I have so far. The ignition to the NO on the Press Switch then the NC to the Positive side of the battery then the C on the press switch to the relay but What point ? there is 30, 85, 86, 87. then from the relay to the battery(pos?), then from the relay to the fuel pump(pos?) than from the fuel pump to battery(neg?) is this correct?
ps. I have a fuse between the relay and the battery and between the ignition and the press switch.

[Caspr49]

I have a holly red pump on a 1949 pontiac with a 1983 inline 250 six cylinder turns off as I am on freeway ten fifteen minnets into the ride I wait five to ten minnets pump starts to work like nothing happend does any body have an idea what's going on with the pump.