Idiot Light/Gauge Sender Question

[1987 GMC Jimmy]

I was wondering if anyone has used a multimeter to tap into the dummy light and gauge senders to get a resistance figure that can be translated to an oil pressure or coolant temp value. This is, of course, assuming the sender works and that the gauge/light is disconnected, broken, reading incorrectly, etc. If so, does anyone know what the resistance ranges are for both types of gauges and both types of readouts(light vs gauge) and how they translate to temperatures and pressure values? I know I can check both with either a pressure gauge or a infrared temp gun, but I was curious just the same.

 

[MikeB]

For idiot lights, there are no senders with varying resistance, just switches.

If oil pressure is low, the oil pressure switch closes to energize the idiot light.

Same for the coolant temp, except the temp switch closes when the coolant reaches some high temperature.

So, the only way to know at what pressure/temp the switches close and light the lamps is to install gauges, which either use senders that vary their electrical resistance OR mechanical gauges with their pointers driven by pressurized gas (coolant temp) or actual oil pressure.

As for senders' pressure/resistance and temperature/resistance curves, you may be able to find some info on the Internet.

 

[1987 GMC Jimmy]

Ahh, okay. That's exactly what I needed to know. Thanks.

 

[RustyPile]

Here's a thread I started recently, concerning temperature gauges.. A chart for converting sending unit resistance to coolant temperature is in one of the posts.

http://www.gmsquarebody.com/threads/temp-gauge-issues.19919/

 

[1987 GMC Jimmy]

Thank you!