77 Truck - Oil Pressure Gauge Inop

I am trying to run down my factory oil pressure gauge which isn't working. I was surprised to find battery voltage with "key on" at the sensor wire, should that be 12v or would it be coming from the dash regulator at ~6v?

How the regulator works is that current flowing thru it heats up a bimetallic strip that opens a set of contacts, the strip cools and the contacts close, etc, etc. averaging ~6v at the output. With the sender disconnected there is no current flow, the strip doesn't heat up, the contacts do not open up and you will read system voltage, be it battery or alternator. YOu sure you have a pressure sender not a switch? The sender is like a metal can, the switch is plastic.

Do you have a temp gauge? Does it work? If so the IVR is ok.

Temp gauge and fuel gauge don't really work, well. The fuel gauge never goes past full, which could be a sending unit problem, to be determined.

Temp gauge pretty much doesn't work at all, if I ground the sending unit wire it is slow to peg, but it will peg.

I do have a can sending unit and a pressure gauge on the dash, no warning light.


I bought a new sending unit and a solid state voltage regulator to throw at it. We'll see if I get anywhere.

I would suggest that if you are pulling the instrument cluster anyway, replace all the dash light bulbs and bulb holders with new.

Temp gauge is not a fast mover, none of the gauges really are. If it pegs with the wire grounded but otherwise doesn't work sender issue.

If you have access to resistors you can test the gauges.

74 ohms = low
23 ohms = mid scale
10 ohms = high/full

One end to ground, other end to sending wire. Note they are not super precise either.

Same resistances for all three gauges.