Chevrolet Repair: oil pressure relay location?, oil pressure switch, fuel pump relay

Question
I have a 1994 chevy ck2500 with a 305.  It had been cutting out and the manual said if i disconnected the relay on the firewall and the truck died that the oil pressure relay would be the culprit. Unfortunately I haven't been able to locate it.  I found the knock sensor and such I know what it should look like but I just can't find it.  In other posts people mention changing it but not where it is.  I thought it was supposed to be next to/over the fuel filter but I haven't found it yet.

Any help help would be greatly appreciated; though I feel retarded not being able to locate.  It's the one sensor not shown in the haynes manual.
Thanks
Chris

Answer
Hello Chris,
There is no oil pressure relay.
I assume what someone was telling you about is the fuel pump relay.
It operates the in-tank fuel pump whenever it is getting a crank signal, meaning the engine is rotating.

There is a backup system to supply battery power to the fuel pump, and that is an oil pressure switch.
Whenever there is oil pressure, meaning the engine is running, the switch is closed, and power goes to the pump from both systems.

true, if the oil pressure switch is bad, and you disconnect power to the fuel pump relay, it will die.
But that probably wouldn't cause the engine to cut out, because both systems would need to fail for that.
The fuel pump relay is in the fuse block looking thing under the hood.

Van