Fuel Gauge not working
I'm here looking for help. You may be the smartest man in the room but feel free to drop out of the conversation if you're going to be an asshat
I asked you a question and you ignored it. This forum is a two way street. NObody pays ANY of us to stop in here. Your statement claiming something special is mostly incorrect, at least for most of the basic wiring. I don't keep up with the options but over the years some cars could be had with the optional Rallye cluster. We need to know IF YOU HAVE THAT. The reason is simple. The Rallye clusters have the regulator device that operates the gauges, INSIDE the fuel gauge
What gauges does your car have? Does it have a factory OIL PRESSURE gauge? If so you have a Rallye cluster. If it only has a fuel, temp, and ammeter, and a warning lamp for oil pressure, it is the "standard" gauge.
The 72 Plymouth manual over at MyMopar will suffice for most of the wiring in the car.
The basics of the gauges: This includes temp and fuel, and oil pressure on Rallye clusters, except the location of the regulator device. These are variously called "gauge limiter" or IVR or "instrument voltage regulator"
Basically you have power from the ignition switch fed to the cluster, powering various items, as well as the instrument limiter. That feeds REGULATED power of sorts to the temp and fuel gauges, which are a "hot wire" type of thing, that operate on approx. 6V pulsating
From there each of the gauges sender terminals go to ground through whichever sender we are working on, IE temp or fuel.
You wan't to be careful as you can damage the gauge units, as well as the IVR SOMEONE ALREADY mentioned to access the fuel sender wire at the tank, devise a way to ground that, and then turn the key to "run." The gauge should quickly peg. Don't allow it to be connected more than necessary. If the gauge pegs, I would start with a gummed up fuel sender.
If nothing happens, try the same thing with the temp sender in the engine bay. If it does not move, you likely have a problem with the cluster PC board, a wiring harness issue, or a bad IVR.
WE STILL NEED TO KNOW if you have a standard or Rallye cluster