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TR2/3/3A Why is voltage stabilizer not needed for TR3 fuel gauge?

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T

TuffTR250

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Two questions: 1) Why does the TR3 fuel gauge not require a voltage stabilizer whereas the TR4 fuel gauge requires one?
2) When I installed an alternator (which bypasses the control box) I noticed that I am getting 14.6 volts at the ignition switch when the engine is running. I did not measure the voltage at the ignition switch before installing the alternator. Will the 14.6 volts at the ignition switch adversely effect the fuel gauge reading since it gets it's power from the ignition swtich ? Do I need a voltage stabilizer for the fuel gauge on my TR3 since I installed an alternator and bypassed the control box? Thanks!
Bob
 
The TR3 gauge uses a 'balanced' movement, that is relatively insensitive to variations in voltage. It will work fine on 14.6v. No VS required.

However, it does need a secure ground at the gauge (also unlike the tr4 gauge). I suggest running a ground wire from one of the gauge mounting posts to the tie point on the back of the instrument panel.
 
If you would like to know more about how the tr3 gauge works, there is a good article at https://www.mgaguru.com/mgtech/electric/fg_01.htm

The MGA gauge isn't quite identical (resistances are slightly different) but the principles are the same.
 
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