My 70 malibu has a three gauge set with a water temp, volts, and oil pressure on it. My question is when the car is on the volt and temp gauge work fine but the oil one is always pegged at 100psi. I replaced the sending unit a year and a half ago because the idiot light came on, and it went back off once i put the new sending unit in. why do the other two gauges work fine with the idiot lights but the oil one doesnt? any ideas? I checked the connections and they all seem fine.

Ernest,
The "idiot" light and the gauge use different sensors. If you are tyring to use the same sensor for both, it will not work. The idiot light sensor is a simple on/off switch. it turns the light on when the pressure drops below a certain point. The gauge uses a sensor which is basically a variable resistor. The lower the oil pressure, the higher the resistance. A good test would be to disconnect the wire from the sensor. If the gauge goes to "0" then it is probably ok. If you touch the wire to ground, the gauge should go to the highest pressure reading.
I dont know if this helps any, but I hope it does,

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

If it's an electrical gauge it sounds like it's grounded somewhere.

Disconnect the wire from the sensor and make sure the terminal isn't touching metal anywhere, then check to see if the gauge is still pegged. If so, your wire is grounded somewhere. If not, you have a faulty sensor or the wrong one.

Edit: Bill, ya' beat me to it. http://www.chevelles.com/forum/smile.gif

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Chad Landry
TC Member #643
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'68 El Camino

[This message has been edited by cjlandry (edited 02-05-2002).]