Fuel pump relay with oil pressure saftey switch wiring question, Scotty?

[Guest 350zgto]

V8 240 conversion. Holley pump. Pump is wired to start on ignition and to oil pressure safety switch via the + coil. Everything works fine. Then I decided to add a relay to the pump circuit. The relay activates and the pump comes on fine with the ignition switch. Here is the problem...when I turn the circuit off (with the ignition switch), the relay remains activated and the pump continues to run. I have to manually disconnect the battery power to the relay to get the relay and pump to shut off. Even after removing the wire that is switched to activate the relay, it continues to remain activated and powering the pump. The relay and pump will not shut off when the ignition switch is turned off. Scotty I know you installed a fuel pump relay, and racing your car you are probably required to run the saftey shut off switch too. I would appreciate hearing from anyone who is familiar with this.

[Guest PROJECTRB240SX]

Are You Sure Your Relay Coil Is Wired To A Ignition Hot Circuit And Not Direct Battery? IT SOUNDS LIKE YOU HAVE YOUR BATTERY CONSTANT AND IGNITION HOT BACKWARDS AND POSSIBLY TOUCHING..... SO THAT YOUR RELAY IS ALWAYS ENGAGED AND WHEN YOUR KEY COMES ON IT FIRES THE PUMP AND KEEP IT GOING.

 

It Should Be Pin (85 Ignition Hot, 86 Ground - These Two Can Be Reversed), 30 Is Your Common Or Battery Constant Hot, And Pin 87 Should Be Your Fuel Pump Power TO THE PUMP.

[Guest 350zgto]

Thanks for your response. The relay is a 5 pin "Painless Wiring" job. It has 4 wires. A ground, a "to pump", a "to battery" and a "to switched source". The ground I am sure of, to pump is wired to the pump, the battery source is hooked up to 12 V hot with the ign switch "on". The "to switched source wire" I am connecting to start position from ign switch. Everything is fine except the relay/pump will not quit running until I turn off the ign switch. I want the relay/pump to stop through the "switched source" wire connection when the ign switch is no longer in start position, like the engine has started and is now running. I want the oil pressure safety switch to take over.

[Guest PROJECTRB240SX]

So You Want To Use Engine Vacuum To Draw The Fuel Into Your Engine? If Not The Fuel Pump Should Be Active The Whole Time The Engine Is In The 'on' Position Or While The Distributor Is Firing.. The Oil Pressure Switch Is Normally Just A Ground That Will Break The Current From The Ignition Switch To The Pump If Pressure Falls Too Low. That Should Be Wired Into Your Switched Source Between Your Key And Your Relay. The Battery Hot Should Be A Direct Battery Wire (it Doesn't Have To Be But For A Consistant 14.4v It Should Be).

 

Whats The 5th Wire Or Connection?

[Scottie-GNZ]

Your description of how you have it wired could lead to misintrpretation so here is what I suggest:

 

- Run a 10-gauge wire from the "to battery" connector on the realay DIRECTLY TO THE BATTERY or a connection off the battery, not the ign switch. Do not use any orignal Datsun wiring except to trigger the relay.

- Run a 10-gauge from the "to pump" connector on the relay to the pump.

- Use the original wire that used to power the pump and connect it to the "switched source" on the relay.

 

Not sure exactly what you are using for the low-pressure switch, but run the original wire that goes to the "switched source" on the relay (also referred to as the trigger or "85") or the relay ground through that oil-pressure switch. With this setup you will have 12V going to the relay all the time but will only get to the pump when you turn the ign on, just like you did originally. If the oil-pressure gets low, you disrupt the relay.

 

Pretty much the same thing Projectrb240sx said.

[Guest 350zgto]

The pump is wired with an oil pressure safety switch. With the engine not running, the relay/pump are on with the ign switch in the on position, they should not be on because there is no oil pressure. When the relay is not wired into the circuit, the pump does not run with the engine not running (no oil pressure, ign switch in on position) this is how it should be. System works fine without the relay. By adding the relay, it is running the pump even though there is no oil pressure and even after disconnecting the "switched source" wire from the relay to start on ignition, the relay/pump continue to run. I cant get the relay/pump to shut off without turning the ignition switch off, that defeats the purpose of the oil pressure safety switch. The relay has only 4 wires, the plug in relay itself has 5 pins.

[Guest 350zgto]

Just saw your post, thanks. I will study this tonight.

[Guest PROJECTRB240SX]

"i See" Says The Blind Man To The Deaf Dog.... I Understand Your Issues Now. Your Oil Pressure Failure Switch Is It The Three Wire Style Or Ground To Block Style? Alot Of The Older Ones Are Ground To Block And In My Experience Sometimes Don't Work Properly..... The Three Wire Ones Are The Best Because It Has A Definate Current Path. I Would Investigate To See If Your Oil Pressure Switch Is Working Properly, Or If You Have It Truely Wired In Correctly (not Saying It Isn't But Its Worth Double Checking).

[Guest 350zgto]

It is a Mr. Gasket 3 prong type. It looks alot like the Chrysler one in the JTR manual, except the "left side" prong goes to the solenoid, rather than to a warning light as the Chrysler has. I am not using the solenoid prong. So I have 12V from + coil in the "top" prong, and 12V from ign switch start position on the "bottom" prong to operate the pump while cranking/low oil pressure. It worked fine till I wired in the relay for the pump. With the relay wired in, I have overridden the oil pressure safety circut somehow, I think. The relay/pump come on when the "switched source" wire from the relay is energized by the start position ign switch, just like it should. But rather than the relay/pump then shutting off (no oil pressure, engine not running), when the ign switch is backed off from start and now in the on position, (where the ign switch would be when the engine is running) the relay/pump are still on and running. I have to turn off the ignition switch to stop the relay/pump. The relay/pump should not operate when the ign switch is in the on position without oil pressure.