[TR] TR3 Fuel gauge test

Randall tr3driver at ca.rr.com
Sat Jan 12 17:29:36 MST 2008


> Well I ordered a new sender unit from Moss & when I tested fresh out  
> of the box I got 0 Ohms resistance no matter where I moved 
> the float.   

Ok, so it's bad or shorted somehow.  Not sure how the repros are made, but
on the originals there was a fiber washer on the stud where the sender wire
goes.  If that washer is missing, or mistakenly replaced with steel, it will
cause a short.  But since it's a new unit, it should be assembled correctly
... I'd just return it.

Except ... (I've got to say this) ... are you sure your ohmmeter is on the
ohms (x1) scale and not Kohms or Mohms ?  And that it works properly ?  I'd
try measuring something else, like maybe between the terminals on the fuel
gauge, to see if it gives a reasonable reading there.

> But given that the resistance device sits down in the 
> gasoline I thought I would try in in my 2/3s full tank.  
> Still getting 0 Ohms.

The resistance device is usually out of the fuel, so hopefully not affected
at all.

> Before I called Moss I wanted to test the gauge as well.

The directions at 
http://mgaguru.com/mgtech/electric/fg_10.htm
are great.  Written for an MGA, but it's gauge is nearly identical to the
TR3.  As you'll see there, he suggests two 68 ohm resistors, which you can
connect in parallel for half scale (34 ohms).  The resistances might not be
exactly right for a TR3A, but you're never going to get 1% accuracy anyway.

Randall


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