TR2/3/3A TR3A FUEL GAUGE

[TR3TR6]

I have a question for the group. Can a TR3a fuel gauge be tested by just applying a 12V source to it? Since it normally receives it's power through the fuel sender unit which has a built in resistance, I was wondering if a 12v high amp source wouldn't just fry the meter. Has anybody tested a meter with just the battery?

 

[PeterK]

You CAN test it by measuring the resistance with an ohm meter across the terminals. It should change as the float is moved up and down. But can't remember the ohm correct readings as it swings through its motion. I'm sure someone will chime with correct ohms.

 

[TR3TR6]

Peter:
Thanks for the reply. But the gauge is not wired up to the sender unit. I was wondering about testing the gauge as a stand only unit.

 

[Adrio]

I can't remember how long ago, but if you search here in the forum someone posted a link to a good article on testing that guage. I think the article talked about builing a resister box to "calibrate" the guage. Maybe someone with a better memory or the actual article link can chime in. wait, I may have found the link https://mgaguru.com/mgtech/electric/fg_01.htm

 

[TR3TR6]

Adrio:

That's a good article on the fuel gauge, but it didn't say anything about just applying a 12v source to the gauge as a method to test it. Thanks.

 

[Moseso]

Also --
The TR3 gauge works "backwards." A full 12 volts makes it read empty, though the needle will come up off the peg. The TR3 sender is high resistance, when full -- low resistance when empty.

One more thing -- as well as hooking up the battery to the terminals, the case must be grounded. The needle will move around if the case is un-grounded, but it won't read correctly. Don't ask me how I know this, nor what the result of that failed experiment was...

 

[MGTF1250Dave]

Aloha,

A power source for a simple "does it work" test is a 9 volt battery. The old transistor radio battery with some leads attach will be enough to show you the electric gauge needle will react to power. It will not determine accuracy, but the low voltage and amperage won't hurt the gauge.

 

[TR3TR6]

Thanks everybody for the info.

 

[TexasKnucklehead]

According to my notes:
TR3 fuel sender = 2 ohms at empty (that's basically a short or direct connection)
TR3 fuel sender = 85 ohms at full

So, if you hook one side to a 9v battery (or 12v dc source) and the other to a 85 ohm resister with the resisters other end to the other side of the supply, you should see full. Remove the resister, and see empty.

Early TR4 fuel gauges look the same, but empty=240 ohms and full=30 ohms.