my 78 macho has the gas guage gone out, it did work for a bit then had to tap the guage to get it to work, then bang on the dash, then came and went and now its completly off just reads empty all the time, i bought a new aftermarket gas gauge and hooked it up and it just reads way past full all the time never anything else, i routed the power from the batt and grounded to the frame and then to the sender, all with alligator clips and jumper wires so i could see if it was really gonna work before i went thru the hassle but it just reads full all the time. i think my sending unit is bad? i called the help line and the guy was useless he had no info just wat he could punch up on his computer. now my other issue is if my sending units bad and i cant find another would a ramcharger tank fit up in my truck with some rigging? i can make anything work so dont be afraid the throw ideas

If your sending unit is bad buy a new one from mopar. They still sell them!

not that ive ever seen

Since you banged on the dash/gauge and it worked for a while, I would say the gauge is bad or there is a connection problem. The sending unit works on an ohm grounding ratio. So to test the original gauge when hook up in the dash, take the sending unit wire (middle one) off the sending unit gas tank and ground it on the frame of the truck. Note: the Key must be on RUN position. If the gauge is good it will pin it self to the full peg. Let off the ground and it will move back down to empty...................
Now with an aftermarket gauge hook up the the original wiring harness, it will not be accurate because the Ohm ground is calculated at a different rate than MOPAR...........Once you determine the original gauge is good, then test the sending unit by taking it out of the tank and grounding the outside terminal to the frame. Then hook the middle terminal up to the original wiring harness. Turn the key to run position and manually move the sending unit float up slowly to full up. Look at the Dash gauge. If it's moving the sending unit is good. Now the only other problem would be the float has gas in it. to test: take a one gallon bucket of water and dip the sending unit in it and see if the float stays on top of the water. then its good.
Aftermarket fuel gauges need the aftermarket senging unit to work accurately.

gauge is bad thanks warlock, good thing i have another dodge truck but its only to 75 mph

i have a bad connection, i just swapped the gauges and nothing grounded the gauge to the frame still nothing, my book shows a blue with black stripe wire to the sender so if i route a wire to that will my gas gauge come back or is there another wire? im just trying to get it to where i can drive it with a gas gauge before i go for a resto with the new bed and all

Best thing to do is check the wire for omes. Use a multi meter. connect the sending wire to the meter then the other side of meter to the gauge. If it goes to infinity on the meter the wires ok. If not, start checking the wire from the harness fire wall plugs to the gauge, down the line untill the short/bare wire is found..etc, etc. Then repair it.

k ill try that and ill get back with you

Revision: If the connection goes to "0" on the meter the wire is ok. Infinity is an open wire. The multi meter when unhooked from testing is in infinity mode. When the meter probes are connected together it should read "0". Meaning a good connection.
Resistance in the wire is acceptable in low reading ohms on the meter. All metal (copper) wire have some resistence omhs.

mines a digital meter so should it read ofl?