Disclaimer: I'm not technical. What are the most common reasons a gas-gauge does not work?

 

1) out of gas
2) wire disconnected (cut or unplugged)
3) possibly a short to ground depending on factors

 

Updating the obvious... Tank levels not a factor!

 

Is this for your 87 waggy?

Is it one of your NOS sending units or mystery part

 

The most common problem with anything is the wires or their connections. Your pump/gauge assembly fits in the front, upper of your tank. Pretty easy to spot. Any work there is best started with a cleaning from the car wash wand, as the crud rains down into your eyes. Anyway, with glasses at least, find the wiring connector to the buisness with the fuel lines going to it, unplug it and spray the connectors with CRC electronic cleaner. Plug, unplug, spray, repeat a few times. It's recommended you remove Battery negative cable to be safe. I likely wouldn't bother myself, but cleaning the battery terminals is something to do now and then anyway.

Besides ruling out that connector as a problem, getting familiar with where it is may help diagnose it down the line. (see if you can make out the color codes)

Has it ever worked? Oh...waggy. I have a couple with mechanical pumps on the engine. I jumped to you being Renix.

 

I'm back at the garage working on this... New info: Gauge-needle spins freely.

 

Poked around a bit today... No progress. Trip to the local mechanic for help.

 

What I learned: The gauge-needle is moved by magnets driven by 1-ohm to 88-ohm(full-tank). Applied voltage... Watch the needle go ♬ up-and-down, up-and-down ♬. Cleaned terminals on sending-unit and applied dielectric-compound. All is good in Désirée land again!