American Motors: 1979 Jeep Cherokee Gas Gauge, jeep cherokee, gas gauge

Question
I have a 1979 Jeep Cherokee and the fuel gauge reads empty.  I've traced the wire from the sending unit to the firewall and when I put a meter on it, it reads about 80 ohms (which is about the amount of gas in the truck).  So the resistance is correct.  So I put my dc voltage checker (probe) on the wire (other end to ground obviously) and with the switch on the light starts blinking and the gauge starts to work (I believe I'm just sending the gauge to ground).  When I put my meter on the connection the meter reads a constantly changing 0 to 3 volts.  I have no idea if this is normal, nor why I'm getting a constantly changing voltage.  The bottom line is I would like to know what to do to make the gauge work...any idea what is wrong?  Thanks, Pete

Answer
1) Disconnect the sending unit wire from the tank and ground it.
2) Turn the ignition key on.
3) If the gauge goes to full, the gauge is OK; replace the sending unit. If the gauge does not go to full, replace the gauge. There is also a constant voltage regulator on the circuit board, Usually, if it is bad, other gauges will malfunction.