[TR] TR3 fuel sending unit impedance

[Randall]

> I have a question regarding a '60 TR3 and the fuel sending 
> unit, when  
> I connect the fuel gauge it is pegged to full, 

First thing to note is that the gauge housing must be grounded for proper
operation.  Without the ground, it may peg either full or empty, regardless
of the sender resistance.

> When I measure the  
> impedance of the sending unit, with the tank empty it shows 82 Ohms.  

Then either a defective or wrong sender.  On a TR3 sender (which is unlike
TR4-6), the empty resistance should be near zero.

> I would like to know what the sending unit should measure when empty  
> and full, so I have some idea where to go with this problem,  
> additionally any other information regarding this problem would be  
> appriciated.

There is a very detailed article at
http://mgaguru.com/mgtech/electric/fg_01.htm
with more than you ever wanted to know.  Written from an MG point of view,
but the gauge is basically identical to the TR3 (although the resistances
might be off just a bit).

If the back of your gauge doesn't look like the one shown on Barney's site
(with the slots & nuts), you may have the gauge from an early TR4, which
looks identical from the front but works backwards to the TR2-3 unit.

Randall