Two Oil Senders?

[68longhorn]

My 86 C10 has an issue with the oil pressure guage, it stays steady around 20 psi whether the engine is on or off. Occasionally it might flutter but mostly stays still. I want to check my sender but there are 2 of them? Under the distributor there is a split and one larger one points to the passenger side with 1 wire, and another points to the driver side with 2 wires. Which one is for the guage and how do I test it?

[ray_mcavoy]

The larger sized one with the single wire (should be a tan wire) is the sender for the gauge.

You can test the gauge & wiring by simply unplugging the wire from the sending unit. Turn the key on and the oil pressure gauge should peg to the maximum (or a bit beyond). Next, hook a temporary jumper wire between the unplugged sending unit wire and ground. Turn the key on and that should make the gauge read zero. If this all checks out okay, you are most likely dealing with a bad sending unit.

For additional testing, you can connect a multimeter (set to the resistance scale) to the sending unit (gauge wire unplugged from the unit, one meter lead to the sending unit terminal, the other meter lead to a good ground). With the engine off (zero oil pressure) you should see a reading close to zero Ohms. Then with the engine running you should see a higher resistance reading that varies with the oil pressure. For a 60 PSI gauge (the most common), expect to see about 45 Ohms for approx. 30 PSI of oil pressure and close to 90 Ohms for 60 PSI.