What Are You Doing To/With Your Car Today?

Today I'm chasing electrical gremlins and trying to learn how to use an analog multimeter. Pops put this together from a kit back in the 80s and ended up gifting it to me.fullsizeoutput_8c9.jpeg

My fuel and water temp gauges have never worked since owning the car, and while I went with an aftermarket water temp gauge, I'd still like to have an idea of how much gas I've got. I check the ground at the sender, looks good. Replaced the voltage regulator with an RTE limiter and soldered some damage on the circuit board, no change.fullsizeoutput_75c.jpeg
Yesterday replaced the circuit board with a new one, still no change.fullsizeoutput_8c8.jpeg
I'm considering starting a new thread about this, but should the tab on the voltage limiter be connected electrically? Or does it simply "plug" into the back of the instrument cluster like I have it in the picture?