20mercury

Working on fixing my oil pressure gauge on my 76 and discovered the gauge appears to be ok but the resistor that is on the back had a broken wire.

Where can you get another resistor like the original or I suppose any resistor will work if you know the right ohm size??

Or just for fun, I took off and checked the similar looking resistor on the fuel gauge and it measured about 96 ohms. Is the resistor on the fuel gauge and the resistor on the oil gauge the same part?

Thanks.

toddalin

If there are no numeric markings on the resistor, you can use the size (for wattage) and band color code for impedience.

A 100 ohm resistor is coded with brown (1) (1st digit), black (0) (2nd digit), brown (x 10) (multiplier) bands.

Just remember "Bad Boys Rape Our Young Girls But Violet Gives Willingly."

For safety, your resistor is probably rated for 2 watts, but could be just 1 watt if the gauge does not receive full voltage.

(13.2v x 13.2v)/100 ohms = 1.74 watts

20mercury

Thanks for the info!

7T1vette

The wire-wound 'special' resistors on the C3 gauge cluster aren't coded, if I remember correctly. To get a good estimate of the resistance, lift the two ends of the broken wire (so that they are apart from the rest of the wire) and clip a paper clip across them to complete the circuit. Then use an ohmeter to measure the resistance of the entire resistor (the paper clip resistance will be negligible). If you go to Radio Shack to replace it, buy a 5 watt resistor as a substitute; there is a decent current dropped across that resistor.

jotto

From what I remember from Ernie at Willcox ( hopefully he or roger will chime in soon ) The number 90 seems to ring bells. I would guess that the resitors are all the same value and so a 90 or 95 ohm resistor from your local electronics store would be fine.

If you had a way to accurately measure the oil pressure, you could get a variable resistor and tune it to match your gauge with the 'real' reading.

...Roger...

Jotto is right ,90ish is close. I've measured a bunch and I think it depends on temp also. The ones I've measured have been between 83 and 95 ohms (notes are not with me). I've always wondered if this resistor is custom fit to match the windings in a particular gauge.
Changing the resistance of this resistor does change where the needle sits on the gauge.

7T1vette

I'm sure there was no "custom fitting" of resistors for gauges in production GM vehicles (piston sizes were select-fit for Cadillac engines; but that's a different story). The oil pressure gauge was not meant to be very accurate...just repeatable.

20mercury

Thanks for the info.

I have measured the oil pressure with a pressure gauge, so I know I got 40psig, but it would be nice to have an indication on the dash. I will pick up some 5 watt resistors in this ohm range and see if that does the trick.

Thanks again!