Where to hook up mechanical oil pressure gage?

[Jason Spears]

I'm in the process of hooking up a mechanical oil pressure gage in my truck and I'm not sure where to hook it up. I have an '87 1/2 ton with a 305 TBI. There are two oil pressure taps on the engine. One is beside the distributor and the other is just above the oil filter. The one beside the distributor has two wires going to it and the one by the oil filter has one. I have all of the factory service manuals and wiring diagrams but they seem to contradict themselves as to the function of each of these switches. One switch is a oil pressure switch which gives a permissive to the fuel pump to come on once the oil pressure reaches 4 psi. The other is a sending unit for my idiot light. Now according to the wiring diagram the one with two wires (beside the distributor) is the switch for the fuel pump and the other is for the idiot light.

In the section on the instrument cluster in the service manual it says when you have a problem with the gages to check the sending unit beside the distributor. I've also read in other posts about a tee fitting beside the distributor in trucks with factory gages. Is the other switch present in trucks with gages?

Where has everyone else hooked up their pressure gages? I just want to make sure I'm getting the correct reading so I can diagnose my oil pressure problem correctly. Thanks for the help.

Jason