Idiot Lights to Gauges

[ray_mcavoy]

Originally Posted by Bmstd

Well, I tried to test the oil sending unit with my ohm meter but could not achieve readings consistant to what you have provided me as a guide mr. ray_mcavoy.

Out of curiosity, what were the readings you obtained?

Originally Posted by Bmstd

Another descrepancy i found when re-pinning the plug for the cluster is that the terminal guide provided states that the oil light/gauge light wire is supposed to be blue, but the truck wiring for this is tan, and so is the wires that were sticking out of the plug from the donor gauge cluster.

GM made some changes to the wire colors sometime during the 1978 model year. That terminal guide you looked at must be using the older colors. Tan (as you found on your truck) is the correct color for the late 78 & newer oil sending unit circuit. Another color discrepancy you may have noticed is the fuel sending unit wire (that one changed from tan to pink)

Originally Posted by Bmstd

You are correct, the truck wiring originally used the dual terminal plug for the oil warning light and control for electric choke. The wiring harness also contained the extra plug in for the single terminal oil gauge sending unit which is the only thing i have connected.

I took a closer look at the GM wiring diagrams and it appears as though that single terminal plug & tan wire are present on all trucks. But with warning lights, it is simply left unused and the wire dead-ends at the firewall bulkhead connector.

On trucks with e-choke & warning lights, the tan wire in the cab harness is actually connected to the dark blue wire in the engine harness that goes to the 2-terminal e-choke/oil pressure switch.

On trucks with e-choke & factory gauges, GM placed the tan wire in the cab harness into a different cavity in the bulkhead connector. In that location, it does connect to the tan wire in the engine harness leading to the single-terminal plug for the oil sending unit. And they added a dark blue wire to the cab harness to operate the "CHOKE" light at the bottom of the speedometer in the gauge cluster.

So without also re-pinning the tan wire on the cab side of the bulkhead connector, the oil gauge will still be connected to the e-choke pressure switch plug instead of the oil sending unit plug.