Petrol and temperature guages not working

[Brian75]

Petrol and temperature guages not working on my 2B with pinto engine and Sierra loom. Doesn't look like they go through the fusebox but need to understand this as well. Any way of testing the sender units or other pointers before I take it apart?

[MAHATMA]

faulty voltage stabiliser?

[Brian75]

Thanks Mahatma, that's what I've been advised of elsewhere as well. I was looking for something that was common to both gauges and it looks like this is the first place to look 

[nelmo]

Senders work by changing their resistance as whatever they are measuring changes, so put a multimeter between earth and the sender signal wire, note the resistance at one setting (low petrol or low temperature), then increase the levels (fill the tank and run the car for a while) and measure again. If the resistance has changed, then it is doing something - although no guarantee it is changing correctly   - but it's a start.

In my experience, senders rarely stop working - it's always a wiring issue and most often, a bad earth. My temp gauge stopped working for months, spent ages trying to fix it and finally noted some dirt under the screw head that held the earth wire on. I couldn't believe that was the problem (there is the rest of the screw bodv in the thread making metallic contact, no?) but no - cleared the tiny bit of dirt away and voila, gauge working again.

[Sparepart]

In the attached diagram, d and e are the temp gauge and fuel gauge, you can see that they both draw power from f, the voltage stabiliser. This power then runs to earth via the sensors, 27 is the fuel gauge sender unit and 26 is coolant temp sensor. As you can see it is only these two gauges that use the stabilised voltage, so if the stabilser fails these gauges will malfunction. You could also test that power is getting to the stabiliser, check F8 in the fusebox, and for power on the Black/Yellow wire to the instrument cluster, with the ignition on. Actually if there is no power on black/yellow other things wont work, like the oil pressure warning light (j/28), so if this is working there should be power to the stabiliser.

Edited July 14, 2023 by Sparepart
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