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Freddy 94 nv 3500 2x4 Cheep beater.

Truckman4life

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I looked at a schematic and it does have an oil pressure switch and also a relay. It looks like it starts on one power source from the oil pressure switch then the relay connects and also powers it at the same time or maybe the relay powers it at first then it switches to the oil pressure switch, I'm not sure. It also has a wire ran to a terminal on the DLC connector under the dash. You could easily put power to that terminal and it will run the pump then see if it starts easier but it looks like that circuit goes open when the relay gets energized. First schematic is with an ECM and second is with a PCM not sure what you got. They are similar. The PDF is the whole powertrain management in color.
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  • Fuel pump wiring.pdf
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dhcomp

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I always thought the oil pressure circuit is just a backup for fuel pump relay. Shouldn’t be the primary setup.
 
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