Is there a certain place to attach a ground wire from the sending unit to the chassis? Was it bare wire or insulated? I know these are dumb questions but I want it to be perfect. LOL
I agree with Tiny. My ‘37 coupe does not have a separate ground wire.
However, we added a ground wire on my friend’s ‘49 3100 truck. We knew that the tank probably would not ground because we installed some thin mounting pads between the tank and the saddles that are welded to the cab floor.
We made a wire with an eyelet connector at each end. One end went under one of the screws that holds the sending unit to the tank. We drilled a small pilot hole and used a sheet metal screw to attach the other end to the truck floor.
The Coupe had no ground wire if you are looking for "correct".
I do like Rusty's suggestion of adding a ground from one of the sending unit screws to some sheet metal since the tank is inside the body. It's hidden under the wood in the Coupe so getting a good solid ground this way would be a good idea.
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette
The tank needs no stinkin' extra ground. If the needle is working right then everything is okay.
Think of it this way: If one wanted to insulate that tank from any possible ground effects as it sits correctly installed in the car, what would one have to do? It would be one heck of a job. Would too!
Now crawl out from under there and polish the chrome on the hubcaps or something else more meaningful.
The fuel line will act as ground unless someone used teflon tape and/or plastic or rubber coated clamps. Paint under the straps is also another reason for poor ground but it does help to keep out the rust. I added the wire from sender to frame and opted to thoroughly paint the tank and straps.
I agree that when these great classic cars were built there were more than enough paths to ground so the fuel gauge system worked as expected.
The suggestion to use a dedicated ground for the sending unit is based on my observations. In our zealousness to "restore" these cars we tend to paint/powder-coat every piece to the max and install anti-rattle, anti-squeak, or anti-wear strips wherever 2 metal parts come together.
For example, in my car have installed an inline fuel filter on the fuel tank outlet. Short pieces of rubber fuel hose connect the steel lines to each end of the filter. There is no opportunity for a grounding path through the fuel line.
AC's gauge design requires that the total resistance of the gauge wire, the sending unit, and the ground, all the way back to the power source to be 0 ohms for the needle to go to "E". We don't live in a perfect world, so 0 ohms is impossible. We can only get close. Close enough that the needle is more or less on "E" when the tank is empty. Worse, if any connection or anything in that loop degrades, the needle will go higher and never drop to "E", leading the driver to believe he has more gas than he does, and probably run out.
Steel laying on steel will degrade over time, and the gauge design requires an excellent ground to work properly. I add a wire from one of the sending unit mounting screws to the frame or body, whichever I think is grounded better (usually the frame). The wire can be completely hidden with the tank in.
Gas gauge was stuck at 3/4 full all the way til i ran out of gas then realized my sending unit is not working. My former 38 Town sedan fuel gauge showed empty until i found ground wire not connected so grounded it to bolt on the frame and the gauge worked going forward. Again, not sure what is going on with my 38 Master sedan, I will access sending unit through a hole cut by the previous owner above the gas tank
I attached a negative chassis wire to one of the fixing screws on the sender on top of tank
Hi there, did your 38 have a hole their from the factory, it looks clean. My 38 looked like the previous owner used one of those old fashioned can openers that rip the metal as it goes along leaving jagged edges.