This site has helped me resolve several issues with my truck (thanks to all your posts!) but I'm stumped on this and could use some help.

My 66 F100 (I6 240) does not have an oil-pressure sender currently. I have the stock gauge cluster and I'm looking to get the oil-pressure light working again. The fuel sender, water temp sensor, and gauge lights all work so I have some confidence that the voltage regulator is working. I can trace a white-red stripe wire from the idiot light in the gauge thru the bulkhead to the engine bay (wire was just flopping around) but when I measure the voltage on it, I get 12V. I had thought the voltage regulator would have cut that to 5V.

Should I be seeing 5V or is this 12V correct? I understand that the white/red wire isn't under load when I measure but I would have thought the load from the other functioning sender/lights would have served that purpose.

Before I just ground out that wire to see if the light comes on, I figured I should check here. And, if that 12V is sign for concern, any suggestions for next steps? Do I have a bad IVR?

Also the oil-pressure sender port on the motor has a plug threaded into it which will need to come out. If anyone has had to remove a similar plug and has experience to share, I'm all ears.

Thanks in advance,
Jeremy

 

It's just as you suspect.

White/red = oil‑pressure warning lamp feed. It is not fed by the IVR. It is fed by full system voltage (battery/ignition). The sender on the block is a simple ground‑switch, not a variable‑resistance sender. The lamp circuit goes from Ignition 12 V to bulb → white/red wire to sender → ground. Meaning with the sender unplugged, the white/red wire will ALWAYS show 12 V. That's your potential voltage or open-circuit potential. With the sender grounded, the lamp lights and the wire voltage drops to 0 V. So, your 12 V reading is exactly correct. You should be safe to ground the wire, and the lamp should light up.

 

Much appreciated @TA455HO !