When my boat was built in '87, the manufacturer installed a Moeller fuel gauge on top of the tank, which could not possibly be viewed by a human. The cockpit was about 2" over the gauge, and this was about 12" away from the lazerette. Here is a pic;
Fortunately, this gauge was set up to be used as a sender if a gauge was installed. Why they didn't install an electric gauge?? I can only guess... You can see the nuts that are used as contacts on the sender.
I installed an electric gauge next to the electrical panel, and initially figured that the ground for the electric gauge light was the ground for the unit.
When I went to try it, no reading... After hours of troubleshooting, and being trained to install gauges by the MMTA (see my signature), I went out and bought a new sender. More hours of installation and troubleshooting, and the I got the same result. "It must be a DOA electric gauge," I thought, and so returned the one that I had been trying to install. I installed a new gauge, same result...
Finally, I noticed the other ground lead on the electronic gauge and connected it. Voilla!