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TR2/3/3A Can a TR4A Fuel Gauge be swapped into a TR3A?


Darth Vader
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Reason I ask is that my TR3 fuel gauge has an open circuit but I have a good TR4A fuel gauge. Is this swap doable or what what would I need to do to make it work? Also was there a difference between the TR4 gauge and the 4A gauge?


Great Pumpkin - R.I.P
You would need a voltage stabilizer, and a tr4 sending unit. I'm not sure offhand, but ISTR the 4A gauges each had their own bulb for illumination, so you would probably want to wire that into the existing dash lights.

Otherwise, I think it would work. Might need to tweak the calibration a bit for different fuel tanks, but it would probably ly be OK as-is.

Early TR4 fuel gauge looked different than the later ones (curved glass vs flat plus the shroud over the needle pivot). Seems like maybe there was a further cosmetic change for the 4A, but not certain offhand.


Darth Vader
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In regard to 4 and 4A gauges in terms of internal electrical they would likely be the same. Correct? Could the TR3A sending unit be modified to work with the 4A gauge? I have a friend that is very good at everything electrical working on the conversion but he is not familiar with these Brit gauges. Is there a big difference in the resistance of the two sending units?


Obi Wan
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You might try taking your TR3 gauge apart and seeing what's wrong with it. If it's like the TR4 gauge, it's easy to disassemble and it uses a heated bimetallic strip, not a conventional meter movement. It might just be that the wire has come loose from a terminal.

Yes, the TR4 gauges have individual lamps.


Great Pumpkin - R.I.P
Tr3 gauge is completely different inside than Tr4. Still might be repairable, though. Two electromagnets, wound with very fine copper wire and a big resistor.

Barney Gaylord put up some very nice pages on testing and repairing an MGA fuel gauge (which is very similar but slightly different resistances). Sorry, I don't have the link handy. Search for "MGA with attitude".


Great Pumpkin - R.I.P
Yes, that's the one I meant.
Thanks, David.
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