[TR] Troubleshooting TR3A fuel gauge

[Randall]

> 
> -       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?

You've got multiple bad connections, in the sense they present some
resistance.  Not at all unusual on these old cars.

The variation is most likely the sender jumping around, but could also be an
intermittent connection somewhere.

I would start walking along the circuit, going point to point along the
conductor instead of each point to ground.  Maybe start with the battery hot
post to the terminal for the brown wire at the starter solenoid.  Then that
terminal to A1 on the fuse block (which should be a direct run of fairly
heavy brown wire).  Etc, etc.  Each time you find a voltage drop,
disassemble, clean and inspect the joint.  

If the drop is happening in the wire, consider replacing the wire.

But my guess is that you have a post-60K TR3A with the Lucar connectors, and
you'll find that all the drops are happening at the Lucar connectors.  They
were never designed to last this long!  Generally though, cleaning the male
tab, smearing a little bit of your favorite preservative on it (silicone
grease or even Vaseline), and pinching the female connection a bit before
reinstalling it; will make a noticeable improvement.  If not, the next step
is to replace the female connector.  Preferably (IMO) with a quality
non-insulated terminal, both crimped and soldered to the wire, then
insulated with two pieces of heat shrink tubing.  I put a short slide show
up at https://imgur.com/a/yETAubD

-- Randall