Everything is new.. cluster gauges, gas tank and sending unit.. It reads past full when the ignition is on... all 12V... do I need a resistor inline for it to work properly.
1954 Chevy 3100 One problem solved doesn’t seem to shorten the list Montgomery, AL In Project Journals
That is pretty indicative of either the wire is off the back of the gauge, the wire is off or not making a connection at the pickup, or there is a break in the wire itself. If you are 100% sure there is continuity, then the gauge is shot.
You don't need a resistor. Especially if you have a new gas gauge and it was designed for 12v. Actually you won't get a resistor anyway. You'd get a voltage regulator, but only if your gauge was designed for 6v...and even if it was designed for 6v if you run it on 12v it won't be long before you re-magnetize the little hourglass in there and once that happens it will re-orient and readjust itself. Until that happens about the only thing a 6v gas gauge run on 12v will do is make the needle travel faster. I think Mike got it...you have a bad connection somewhere (at the sender or gauge) or a wire is broken inside the insulation. Yes, that's rare but I've seen it happen. When you have a bad connection between your sender and the gauge, what happens is your gauge runs as far up toward F as it can go. When you ground that same wire (the one in the center of your sending unit) your gauge goes straight to E. Your gauge is looking for a resistance value between 0 and 30 ohms. Having said this, you also could have a bad sending unit. Here's how: your sending unit is a variable resistance device and it sends varying resistance to your fuel gauge by "wiping" a contact point across a resistance wiring. If your sender is bad (made badly in your case) then it is possible that wiping contact point is not touching your resistance wiring. This will produce the exact same result as removing the wire going to the center of your sending unit. I posted an image of an OEM AD sending unit which failed. I had to make a new wiping contact dot from a small screw/nut. The old one had become disconnected and hence it failed to work any longer. Which sending unit did you purchase?
Last edited by Jon G; 07/25/20239:55 PM.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
I don’t remember for sure but I think I got it from classic parts. I’ll look it up later when I get home. I also didn’t have a VOM when I first installed it and had problems.
1954 Chevy 3100 One problem solved doesn’t seem to shorten the list Montgomery, AL In Project Journals
If you have a handheld meter it is easy to see what is happening with the sender. Set the selector to the lower Ohm (resistance) setting ... might be 0 to 200 ohms or something. Remove the wire from the center of the sender unit. Hold one probe to a known good ground and the other to the center post of the sender (you don't need the ignition on for this...you're just testing resistance). With those two connected, sort of rock sideways on your seat and make the gas slosh around some...just a little. Not a tidal wave. If you see the reading on your tester moving up and down (in numbers...ohm numbers, that is) rather smoothly that's a good sign. If you see any sort of erratic action (numbers going from maybe something like 20 ohms back to 0 and then bouncing back to 20 or something as the gas moves back/forth) that's a sign your sending unit may not be working as it is supposed to...or it could be a sign you're not keeping a good contact as you're holding the two probes. Sometimes that's hard to do on a hot humid evening. I have been known to get 2 clothespins to hold those firmly in place. Good luck!
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
or it could be a sign you're not keeping a good contact as you're holding the two probes.
Alligator clip adapters for the meter are your friend here. When I bought my Fluke meter, the clip adapters were bought right along with it.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
I use a real application method for testing a sender. Remove sender, my gauge wire has a spade connector to the sender. I run a separate wire from there to the sender and bring the sender inside the cab with me. Run a ground from under the dash lip. I then move the arm up and down and watch the travel of the gauge inside the truck.
Last edited by Guitplayer; 07/26/20231:29 PM.
~ BD. "You won't find me in an old folks home" Pioneer Florida Cracker 1958 Apache Stepside 1958 Apache 1/2 ton Panel 1959 Apache 1/2 ton Panel
