Fuel Gauge Dead?

**eeyore** · 16th May 2016, 11:06 AM

After a few months of intermittent failure (ie indicator not moving at all) the fuel gauge (PRC3107) on my 1985 110 seems to be - much like the Monty Python parrot - definitely dead. My understanding is that it is usually a wiring or sender issue, however in this case there is 12v to the gauge, earth is good and connectors at the gauge end read 28 ohms across them with a full-ish tank (OE spec is 12 ohms full; 315 ohms empty).

Does anyone have a method for confirming it's the gauge itself that's the problem before I consign it to the bin and begin the search for a replacement? Also, am I right in thinking the OEM's unusual sender unit resistance range means there's no aftermarket substitute for just the gauge?

**JDNSW** · 16th May 2016, 03:36 PM

It should be pretty easy to check the gauge operation by connecting it to 12v, earth, and a resistance of, for example, 28 ohms or thereabout to earth.

The high resistance being at the empty end means that if the wiring is high resistance anywhere, the gauge will read empty all the time, but presumably you are using a high impedance meter, which will show the voltage even with several thousand ohms between it and the gauge. Try the voltage at the sender with the sender connected. If it drops to almost zero, this will confirm a high resistance circuit. And are you sure that the sender is properly earthed?

I'm guessing you have a wiring problem, possibly bad connection at a join or the fuse contacts (although this may operate other things as well, which should also be playing up).

John

**eeyore** · 16th May 2016, 08:29 PM

Thanks John. I'll bench test the gauge with a suitable resistor and take it from there.

Cheers
Simon

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