Oil pressure safety switch wiring help

[hath]

Today I tried my hand at installing a fuel pump relay and oil pressure safety switch, but didn't quite get the result I'm looking for. The fuel pump isn't supposed to run until the oil pressure sensor hits 5 psi, but right now the pump turns the second I hook the ground cable up on the battery, so obviously I've got my constant wrong, but not sure how to make it all work together. This is how I have it right now:

From the relay:

30 - to battery +
85 - to ground
87 - to fuel pump
86 - to "C" on oil pressure switch

From the oil pressure switch:

NC - to starter solenoid
NO - to ignition wire

Any ideas would be great. Thanks.

[Ranchero50]

Use a ohm meter and figure it out with the battery unhooked. Going with oil pressure switch not working correctly.

[MadMike]

Are you using the 'Buick' style of oil pressure switch?

Starter solenoid is not divorced on GM units, but the 'S' terminal is the same.
And remember that both the 'S' and 'I' terminals on the Ford solenoid are only hot when the key is in 'START', not 'RUN'. There are usually a free bullet butt connector for CT 904(or equivalent) or you can create a jumper between the resistance wire CT Ø16 and CT 16, I think it is a green bullet butt connector.

[Thipdar]

Today I tried my hand at installing a fuel pump relay and oil pressure safety switch, but didn't quite get the result I'm looking for. The fuel pump isn't supposed to run until the oil pressure sensor hits 5 psi, but right now the pump turns the second I hook the ground cable up on the battery, so obviously I've got my constant wrong, but not sure how to make it all work together. This is how I have it right now:

From the relay:

30 - to battery +
85 - to ground
87 - to fuel pump
86 - to "C" on oil pressure switch

From the oil pressure switch:

NC - to starter solenoid
NO - to ignition wire

Any ideas would be great. Thanks.

It would help a lot if you'd give some background info... like year, make, engine size, etc.

[hath]

Ok so I did some resistance testing, results were as follows:

NC to NO = 1
C to NC = 000
C to NO = 1
Switch housing to frame = 001

I also did some other testing:

With ignition wire (86)(yellow) disconnected from C on the oil switch, there is no power to the purple (87) or yellow (86) wires at the relay. Not even when cranking. Nor is the fuel pump kicking on.

When I attach 86 to C the pump turns on, and 87 and 86 get power at the relay.

When 86 is disconnected from the oil switch NC and C have power when the key is off.

When the key is on, all three terminals on the switch have power, C, NC, and NO.

All this said, it didn't lead me to any conclusions, but I'm no electrician either. Does this lead anyone to a conclusions?

[Ranchero50]

Follow Madmikes drawings. Your ignition wire from the key switch should go to the Normally open (N/O) side of the oil pressure switch. The Common (C) actuates the fuel pump relay coil. The Normally Closed (N/C) side of the switch is fed from the Solenoids 'S' terminal.

That way the pump turns on when it's cranking and stays on once you have oil pressure. DC electricity is just logic statements. Not really a big deal.

[hath]

Madmikes schematic is exactly how I have my wiring.

[MadMike]

For ease of reference, we'll use the '70 F350 wiring diagram, http://www.fordification.com/tech/wirin ... master.jpg

Ford Starter Relay. 'FSR'
'S' terminal is from the 'start' position on the ignition switch. CT32. Control circuit.
'I' terminal is only powered on when the starter solenoid(starter) is activated. This is to bypass the resistance wire and provide full battery voltage to the coil during starting. This is electrically the same point as the main starter terminal. CT 262. Power circuit.

Buick oil pressure switch. 'BOPS'
'S' terminal is to feed power to when starting, and should only be powered during starting. This is N/C used to bypass the N/O switch to provide power to the 'P' terminal during starting.
'P' terminal feeds the pump. Simple.
'I' terminal is fed power when the ignition switch is in the ON/RUN position. This is a N/O contact that will not make between 'I' and 'P' until there is oil pressure. Then it closes and will be the power supply feed to the 'P' terminal as long as there is oil pressure. When oil pressure drops this opens the circuit killing power to the pump.

'Bosch' relay. 'BR'
30 - This terminal is fed with fused battery voltage. You may have it switched for added protection/theft deterrence, but no need to.
87 - This is the N/O contact. This terminal will feed your desired switched device. In this case the Fuel pump.
87a- This is the N/C contact. This terminal is not normally used in a simple relayed device. It can be used for a lamp to indicate a device(or relay) is off.
86/85 - This is the control coil. Electrically divorced from the other terminals, this is what controls the contacts and is wired in place of the device you normally would directly control.
86 - This is powered by switched power.
85 - This is grounded to complete control coil wiring.

Wiring.
Connect BOPS 'S'(N) terminal to FSR 'S' terminal.
NOTE: If the ignition has been changed from points and FSR 'I' terminal is no longer used, you may use FSR 'I' terminal instead of FSR 'S' terminal as an alternative.
Connect BOPS 'I'(NO) terminal to free butt connector of CT904/904A(green/red) for ON/RUN power.
Connect BOPS 'P'(C) terminal to BR terminal 86.
BR terminal 85 is grounded.
BR terminal 87 is connected to the fuel pump.
BR terminal 30 is connected to fused power, this can be constant or switched.
BR terminal 87a is not used. If Terminal 30 is switched, 87a can be wired to a lamp to indicate oil pressure switch is open. On a vehicle with gauges, this can make for an impromptu oil pressure idiot light. On a carbed car this will come on when the oil pressure drops but the engine may still be running from fuel in the bowl(s). Giving the operator a chance to turn off the engine prior to the fuel running out and possibly causing damage.

Diagnostics.
Hot in OFF(if not switched) would be Terminal 30 on the relay.
Hot in IGNITION ON/ENGINE OFF(KOEO), would be BOPS 'I'(NO); BR Terminals 30 & 87a.
Hot in START would be FSR 'S' & 'I'; BOPS 'S'(N) & 'P'(C); BR Terminals 85/86(relay coil) & 87.
Hot in IGNITION ON/ENGINE ON(KOER) would be BOPS 'I'(NO) & 'P'(C); BR Terminals 85/86, 30 & 87

Think I covered it, let me know if anything is amiss.