I need help! I have a 70 RR with a crazy fuel gage. The issue is the gage pegs 'full' when I start the car. I read most of the these type of posts on the board here but am still stuck. My VR is new (solid state from RT Engineering)& is working. It is working cause I see the blinking red lite on it. Sending unit is fuelly grounded back at the tank (I even added another ground just to be sure), cluster is fully grounded to frame, so now what? I took the sending unit wire off the actual unit back at the tank and the gage still pegs. I also removed the cluster and removed the fuel gage and checked it with a home made D battery gage checker. It seems fine and functioned appropriately. What else can I do? Have I missed something? Please help!
Nuke

If you remove the sender wire and it still pegs yopu have a wire grounded somewhere.Probally in the sender wire to the back.When it removed the gauge should stay at E.Only GM goes dead full if it looses a ground.Thats on of the tests for a Mopar gauge.Ground the sender wire with key on and it should go full.Sounds like its grounding the wire somewhere.Rocky

pull a batt cable off (always a good habit to get into when using the ohm function on the meter). Pull the L connector off of the sending unit threaded nub at the tank & from that wire to a KNOWN good ground you should show either no continuity (infinity) if it is correct & we know it ain't but not zero/several tenths which is a dead short which means that blue wire is improperly grounded somewhere forward from where you are at up to the downstream side of the gauge. EDIT If you show a dead short then unplug the connector behind the dr kick panel which will open that circuit & repeat the test back at the sender. if still grounded then the ground is rearward from the kick panel connector. If not then it's grounded somewhere from the kick panel connector upstream to the round plug in/flat printed circuit board/gas gauge case

RR my bet is if grounded its near the tank.Ive seen a few that rubbed thru the wire near the grommet in the floor.Good idea to test the frt and rear 1/2s.The gauge going crazy intermitenaly though it might be tough to find.If it did it all the time it would be easy.Rocky

Still might not show its grounded.From what he says it dosent do or stay full all the time.Sounds like an intermiten ground possibly from ign system as he says it does it on start up.I know some gauges did move some when you turned the key on.Another question is does it go to a normal reading after it starts?Rocky

I'm reading that to mean when he starts the car it pegs full & stays there while it is running. Nuke straighten us out on that

RR thats why I finally asked.Cant figure if it stays pegged or not.My one Imperial would swing the gauges on ign on then go back down to normal.If it stays pegged then it probally has a ground in the line.Might have fried the gauge even if left on.On another off topic did you get that 2 stroke going?Rocky

All, thanks for the info. Just to clarify..when I cycle the key to on or "acc" the fuel gage pegs to full. It is not an intermitten issue. Now I did pull the L connector off of the sending unit threaded nub at the tank & from that wire to a KNOWN good ground. I got no reading (i.e. infinity resistance). It did NOT ready anything, even tenths.. I then unplugged the blue sender wire at the connector at the driver kick panel and checked it back again at the tank. Same thing..no reading just infinite resistance. I did not pull the wire off the back of the gauge and off at the tank yet as I will do that tonite. Question..how is fuel gage suppossed to be grounded? Is the gage grounded to the cluster?
Nuke

with the kick panel connector unplugged and key on if it then pegs full then it is (improperly) grounded somwhere upstream from the upstream half of the kick panel connector to the downstream end of the gas gauge on the printed circuit. The tank sending unit is grounded via that metal several inch long piece with the jaws on each end that connects the short nipple on the ouside of the sender to the fuel line (it jumps over the neoprene hose). The fuel line is a very good ground. BUT If I'm reading this right you also have no continuity from the downstream half of the kick panel connector back to the L connector that plugs into the sender threaded nub which is a seperate issue? EDIT while you are at it see how many ohms you have from the sender threaded stud to the round metal sender base. should be somewhere between 10 and 70 iirc depending on how full the tank is

Ok..here is the latest... For sheets & grins I hooked up the battery and removed the connector that plugs into the back of the circuit board and checked it w/a test light. I get no lite when I probe the blue wire. The lite should have illuminated, correct? I then disconnected the connector at the drivers kick panel and tested for a dead short between the blue pin of the circuit board connector and the blue wire @ the kick panel. It reads something like 0.05 ohms. So, does this indicate I have a dead short between the connector at the kick panel & the circuit board connector? If so, how do I fix this?
Nuke

If you touched the 2 meter probes to (A) the particular wire end in the round connector that plugs in to the printed circuit board and (B) to the other end of that wire at the driver kick panel and got 0.05 ohms then that line from (A) to (B) has continuity. Now take one of those probes (either one) and touch it to a known good ground (keep the other probe on its' wire end like before) & if you have infinity (no reading) then there is no continuity to ground and no dead short which is a good thing. do the exact same thing on the ends at the rear kickpanel half and the L connector at the tank sender. Some of this is redundant since we pulled the L connector off of the tank sender & it still stayed pegged which tells us the problem is forward from there but I think this will help us. you might ohm the sender threaded nipple to the sender round metal flat (have it on the right ohm scale as it'll likely be somewher from 10 to 70 ohms. Holler back when you can

RR, per your request I touched the 2 meter probes to (A) the particular wire end in the round connector that plugs in to the printed circuit board and (B) to a good ground and got no reading (i.e. infinity). So, this indicates that there is no continuity to ground and no dead short, correct? I then did the exact same thing on the ends at the rear kickpanel half and the L connector at the tank sender. Again, no reading (i.e infinity). Lastly, I did ohm the sender threaded nipple to the sender round metal flat. It read 30 ohms. What next? Thanks for your info & patience!
Nuke.

Yes your first test tells you there is no improper continuity in that gauge to kickpanel line to ground & therefore no dead short. You checked each end of the rear line in question to ground (2 tests) & infinity each time? One test tells the story but no harm no foul. If so then also there's no continuity to ground in the rear (kick panel to tank) line & therefore no dead short. Take the long female pin out of the round connector (the one in question going back to the kick panel/tank sender) & plug the round connector back in & turn the key on & see if it pegs full. As you know be delicate with the round connector/pins as you dont want to bend one of the pins & lightly/appropriately pry the round connector off of the pins evenly. I'm glad to help & almost everything I know came from Moparts & I'm glad to give some back. Patience comes with age/experience. this last test will further isolate the dead short cuz the downstream end (circuit) from the gauge is (improperly) grounded somewhere