Gas gauge always full (1968 Barracuda)
Alternator: Always stays in the middle
Not related to the other gages except by location.
The main problem with the gage labeled alternator is the label. It's named kindof like the Batt terminal on the alternator.
The gage is an ammeter indicating whether the battery is discharging or getting charged.
Operational Check:
Turn on the parking lights. The needle should move slightly toward Discharge.
Turn on the headlights. The needle should move further toward Discharge. (That's about 12 amps.)
Turn off lights.
After the engine is started, running on fast idle, the needle should move to charge. Then gradually move to center.
While driving, the alternator supplies power at rougly 14 volts to everything so no electricity flows through the ammeter (other than for recharging).
Note: The
ammeter connections are always hot. It doesn't matter if current is flowing or not. All the wires connected to the battery are at battery voltage and can flow if you accidently ground them.
- Gas: Rises to full when key turns on, slowly falls to empty when key turns off
- Temp: Always stays at C indicator
- Oil Pressure: Always stays at low indication
On the rally dash (your Barracuda) all of these get power when the key is on.
The instrument voltage regulator provides a pulsing voltage. If you have an analog voltmeter, check what it shows between the temperature gage sending wire and ground. (It's the easiest to access).
Then you could check the voltage at the fuel gage wire connection.
It does sound like a short to ground is likely. Do those checks with the sending wire disconected and connected if the probe tip can be made to touch the the threaded section. Another way is to back probe in the bulkhead connector cavity.
edit: quick first check could be to disconnect the fuel sender wire at the tank. Turn the key to run. If it the fuel gage shows full, there's a short and its not in the tank.
