[TR] Fuel gauge

[Randall]

> Here is an excellent write-up on testing and repair of the system:
> 
> http://mgaguru.com/mgtech/electric/fg_01.htm
> 
> It is for an MGA but equally applicable to our TR3As.

But don't forget that the TR3 uses slightly different resistances.  The
various tests that Barney gives will need to be adjusted for the TR3.

Personally, I rather suspect the problem is in the gauge.  The sending unit
is a variable resistor as you suggested, but it is at maximum resistance for
full (on a TR3, TR4-6 work the other way).  Although not impossible, it
seems unlikely to me that it has the correct, high resistance when full,
then the resistance suddenly drops for some reason.  The gauge uses two
coils and a resistor internally, and can do some very strange things if the
resistor burns out.

Also check that the gauge body is securely grounded.  I found that my fuel
gauge worked much more reliably when I added a short wire from the gauge
mounting stud to the ground tie point on the back of the panel.

-- Randall