[D Butler]

The voltage gauge on my 70 TA is not working. Does anyone have an electrical schematic of connections for the 70 they could share? Also, any ideas on what to check

Thanks in advance

[TA455HO]

Originally Posted by D Butler

The voltage gauge on my 70 TA is not working. Does anyone have an electrical schematic of connections for the 70 they could share? Also, any ideas on what to check

Thanks in advance

The gauge is a simple voltage sensing device. It measures the "potential difference" between a ground reference and the DC main voltage reference. The ground in this case comes from the main dash wiring harness so if everything else is working good in terms of the gauges and only the volt gauge is not working I wouldn't suspect the ground as the first likely culprit. But, it could be the connector.

Ground is a 18 gauge Black wire. Hot is a 16 gauge Orange wire.

Ground is a common ground called the Accessory ground. It's the large black dot near the left side of this picture.

16 gauge Orange wire ties from the main 12 gauge Orange wire that runs from the fuse block to the ignition switch.



First thing I would do, if possible, is to pull and check the gauge. If you apply a known regulated amount of voltage to it you should get the gauge to move. If not, then the gauge itself is likely bad. Here's a few pictures of mine as I apply 10, 11, 12, 13, 14 and 15 volts to it using the bench power supply behind it. You can see both gauges in the pictures.














The horizontal blade is the ground and the vertical blade is for the hot wire.

Chad

[Peter Serio]

Pretty simple gauge. Battery + power on the orange wire with the key on, the black wire is ground. The 2 wire plug is shaped like the letter "T" There is a ceramic based carbon printed resistor on the back in-between 2 of the mounting studs. If this resistor goes bad the gauge will not work. This resistor is not the same ohms as the others on this gauge set. The volt gauge resistor is right around 124 ohms. It is color identified with light blue paint. Hint: You cannot measure it unless you first take it off of the back of the gauge.

When these resistors get old they will sometimes go bad. They are designed to be mass produced and they will usually last the normal life of the car. In most cases 2X "lifetimes." But the way theses were made, they can go bad.


Another issue which I see all the time on 2nd Gen Trans Am gauges are the 4 flat metal "tabs" on the back of this gauge pod (Fuel & Volts). Those tabs will rust & corrode over time. You can't get a good electrical connection trying to plug your car's wiring onto a rusted or corroded tab.