Electric oil pressure guage

[7500Blizzard]

Can I just splice into the plug on the sending unit for this guage? If yes which wire?
The truck is an 87 with tbi. Seems very hard to find any actual wiring diagrams for this specific truck.
Ken

 

[Dave M]

What exactly are you doing? More info required.

 

[7500Blizzard]

Customer bought an American Autowire kit, so rewiring the whe truck. Trying to put all the fuel injection harness into old harness as it doesn't come. The customer had already installed all new autometer guages but didn't hook up the oil pressure guage. The switch on this truck is also secondary power to pumps, so I was curious as to if I could just splice into it and which of the two wires to use.
Any other information for how to wire in the tbi harness would be great also.

Out of 5 rewire kits this is the first one missing so much compared to factory.
Ken

 

[Bextreme04]

Customer bought an American Autowire kit, so rewiring the whe truck. Trying to put all the fuel injection harness into old harness as it doesn't come. The customer had already installed all new autometer guages but didn't hook up the oil pressure guage. The switch on this truck is also secondary power to pumps, so I was curious as to if I could just splice into it and which of the two wires to use.
Any other information for how to wire in the tbi harness would be great also.

Out of 5 rewire kits this is the first one missing so much compared to factory.
Ken

Pics help... do you have the sending unit with the three wire weather pack connector on it? Do you have the single wire sending unit near the distributor and the two wire switch near the oil filter? If you have the three wire weather pack connector it should have orange, gray and brown color wires. Orange and gray are used for fuel pump backup (redundancy) switch and use larger gauge wires than brown. Brown wire is used for oil pressure light or gauge. The brown wire is what should go to the gauge sensor terminal. Most gauges will have Power, Ground, and sensor terminals. It works by sending power on that sensor wire and the sensor will vary resistance to ground on that wire based on pressure, this varies the voltage that the gauge sees and therefore moves the gauge.

 

[Bextreme04]

This might help too. 87 TBI wiring to the ECM

You must be registered for see images attach

 

[Bextreme04]

Also, this thread has all of the wiring manuals for every year square body, including 87.

https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

 

[7500Blizzard]

Bee Beextreme thanks for the info. First pic helps. The drawing in the library doesn't seem to match my harness though lol. Oil pressure sensor/switch is two wire orange and a
tan-brn/white.

And if you would be so kind I'd like to pick your brain a bit more here and there lol.
What is this as it wasn't connected anywhere? It's under the dash

You must be registered for see images attach

 

[7500Blizzard]

And if it helps it has a 747 ECM

 

[Bextreme04]

Bee Beextreme thanks for the info. First pic helps. The drawing in the library doesn't seem to match my harness though lol. Oil pressure sensor/switch is two wire orange and a
tan-brn/white.

And if you would be so kind I'd like to pick your brain a bit more here and there lol.
What is this as it wasn't connected anywhere? It's under the dash

You must be registered for see images attach

I have no idea... it looks like maybe a connector for a relay of some kind? Maybe power window/door lock relay?

The diagram in the library should be the correct one for an 87 TBI truck and engine, as to whether you have a correct 87 Engine and/or truck is obviously a crap shoot. The diagrams are also not necessarily intuitive and there were some options/variations too. Do you have both a switch and a sensor? One near the distributor and one near the oil filter?

 

[7500Blizzard]

l only have the switch by the distributor.

 

[Turbo4whl]

The aftermarket oil pressure gauge requires it's own sender, not a switch. You cannot hook the wires to the pressure switch for the fuel pump. The gauge may work with a factory sender, but if this truck only has a warning light there is no factory sender.

The sender could be added to the oil pressure system. 1/8 pipe "T" at the rear of the engine block. Or 1/4 pipe fitting near the oil filter.

 

[Bextreme04]

Did this truck originally have an oil pressure gauge? Or was it just dummy lights? That would explain why you only have the two wire switch instead of the 3 wire switch/sender. I agree that you can just tee off the port with a sender only, or you could switch to the correct 3 wire sender/switch that should have come on a factory TBI truck with an oil pressure gauge.