[TR] Troubleshooting TR3A fuel gauge

[Dave MacKay]

 Troubleshooting TR3A fuel gauge

Hello:

I’ve been troubleshooting the fuel gauge on my TR3A because it has not been
providing an accurate indication (or even a reasonable approximation) of
the fuel level in my tank.

I referred to a number of documents and old posts about how to troubleshoot
and calibrate the fuel gauge and sending unit (e.g.,
*https://www.triumphexp.com/forum/tr2-and-tr3-forum.6/faulty-fuel-gauge-57-tr-3.1244960/*
<https://www.triumphexp.com/forum/tr2-and-tr3-forum.6/faulty-fuel-gauge-57-tr-3.1244960/>
and *http://mgaguru.com/mgtech/electric/fg_01.htm*
<http://mgaguru.com/mgtech/electric/fg_01.htm>).

I started by looping a clothes hanger around the float in the tank and
reading how many ohms I saw at different levels. What I found was that the
reading fluctuated --- it didn’t stay the same even when I held the float
at one level. I then checked to ensure that the grounds were good (they
were). Before concluding that the sending unit was flakey, I thought I’d better
ensure that I was getting good power to the unit.

That’s where things got weird.

-       I read 7.6V between the sending unit and ground.

-       I read 7.65V between the T terminal of the fuel gauge (which
connects to the fuel tank sending unit) and ground. However, this reading
was erratic; the value would change to, say 4V.

-       I read 10.6V at the B terminal of the fuel gauge

-       I read 10.9V at the A4 terminal of the fuse box.

-       I read 11.9V at the A2 terminal of the fuse box.

-       I read 12.5v between the terminals of the battery.

I’m a bit baffled. I expected that I’d see about 12V at all points. Even if
the fuel gauge was bad, I would have expected to see the same voltage at
the battery, A2, A4, and the B terminal of the gauge. As it is, I’m seeing
a drop of about 2V among them.

What might be causing the voltage drops that I’m seeing? Could it be as
simple as a broken fuel gauge? If so, how could I test that?

Moss lists the fuel gauge as NLA. Does anyone know of another source?

BTW, when I switched my generator for an alternator years ago, I eliminated
the control box (regulator).

Thanks in advance.

Dave MacKay

TR3A s/n 68639L

near Toronto, Canada
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