TR4/4A Tr4A temp gauge doesn't work

[Alex Grant]

I have a 66 tr4a posi ground.Temp gauge doesn't register. I pulled the gauge out and made sure it worked by connecting straight to 12 volts and grounded out .The needle responded by moving all the way over, so that's telling me the gauge works. I have a new electronic pos. ground vol. stab, installed in the car and checking this out with a digital meter the stab. Is putting out 10 volts. I ran a wire from the instrument side of the stab. to one side of the gauge and ran another wire from the other side of the gauge to ground to see if gauge will still move. With the ignition on , the gauge needle will only move a hair. I feel the gauge being grounded out should move all the way over but at a slightly lower rate than being hooked up to 12volts. Can't figure this out.

 

[dklawson]

Your test method in both cases is valid.

Is this a homemade solid-state stabilizer or one of the units like Moss sells? If it is a Moss unit, did you provide the stabilizer case an earth ground?

 

[Alex Grant]

Yes, stabilizer is grounded. Also used a temp gauge from a spitfire to double check my work. I get the same results.

 

[Alex Grant]

And yes it's a moss stabilizer

 

[TR3driver]

Did you check the voltage across the gauge (at the terminals) while doing the second test? I'm thinking there is a bad connection somewhere, so you're not getting 10 volts with the load (gauge) connected.

 

[Alex Grant]

I'll let you know!

 

[mtlman8]

Does the fuel gauge work? My temp and fuel gauge stopped and it was a loose wire at the horn of all places.

 

[Alex Grant]

I hooked the temp gauge up and put a meter between the terminals . The meter is reading 1.9 volts across the terminals.

 

[Alex Grant]

The fuel gauge was not working also, I'm trying to figure this out one gauge at a time, starting with the temp. gauge.

 

[TR3driver]

I hooked the temp gauge up and put a meter between the terminals . The meter is reading 1.9 volts across the terminals.

With the sender lead grounded, right? So now you know you aren't getting 10v to the gauge. Next step would be to check at the VS, input to ground and output to ground.

If the output at the VS looks OK with the gauge connected, the problem has to be between there and the gauge. But if the input voltage is low (which seems more likely), then the next place to check would be at the "green" fuse (fuse #2 according to the diagram I'm looking at). Again, do the test with the key on, gauge connected & the sender lead grounded. Both the fuse & its holder can fail in odd ways, so again check both input and output.

 

[Alex Grant]

Everything looks good as far as input output at VS and checked out the fuses they also check out. Like l said getting 1.9 volts across terminals but getting the 10 volts on the sender side of the gauge which is grounded with ign on. Doesnt make sense to get the 10volts on the sender side but not between the terminals

 

[TR3driver]

getting the 10 volts on the sender side of the gauge which is grounded with ign on.

Then the problem has to be between that terminal and ground (ie the sender wire). If the terminal is properly grounded, the voltage would be zero.

 

[Alex Grant]

I have a wire going from the terminal side right to ground on the battery.

 

[TR3driver]

I have a wire going from the terminal side right to ground on the battery.

But you claim there is 10 volts from the terminal to ground. Either the wire is defective, or it is glowing red hot. Or your measurement is wrong somehow.

 

[Alex Grant]

I know what saying. I must be missing something that obvious but can't see it , at this point just going to live with no temp or fuel gauge

 

[Alex Grant]

Is it possible the ground connected to the gauge that is used for the light has any effect on the function of the gauge?

 

[TR3driver]

It shouldn't, unless there is a short inside the gauge. Normally, the internal gauge circuit (which is just a length of resistance/heater wire) only connects to the two terminals; and the gauge should work fine without being grounded at all.

 

[Alex Grant]

Figured out my problem, it was the volt. stab. Got a new one . But here's a head scratcher, the volt stab that I had was putting out 10 volts when I had a meter on it, but I decided to use a test light in place of the meter and the test light barely lit. Odd.

 

[TR3driver]

But here's a head scratcher, the volt stab that I had was putting out 10 volts when I had a meter on it, but I decided to use a test light in place of the meter and the test light barely lit. Odd.

That kind of thing happens all the time. The voltage drop across a resistance depends on the current through the resistance. (In fact, the equation is given as E=IR where E is voltage, I is current, and R is resistance.) The meter draws effectively no current at all, so even a really bad connection will pass enough current to drive the meter. But a test light does draw some current (100ma or so) so a high resistance connection will make it dim or even not light at all.

This is exactly why I was suggesting you make the measurements with the gauge connected. It draws even more current than the lamp does, so it can be affected by an even lower resistance connection.

 

[Alex Grant]

Makes sense when I had gauge connected to the "good" stabilizer I had, the gauge barely moved even though the stab. Was putting out 10volts. Thanks for your everyone help with this issue. Chasing down electrical issues can be a pain in the a-- at times.