Fuel gauge dead?

So my fuel gauge stopped working a few years ago and about a year ago I had the sending unit replaced at a shop (didn't have time to mess with it myself) and it worked for a couple months and has since died again.
Every blue moon if I really top it off with gas it will come back to life and jump to about 3/4 but then I can watch it fall off a cliff back to empty within a mile or so. I went under it this weekend and smacked the tank (at the bolts for maximum impact) with a rubber mallet to no avail.
When I had the sending unit replaced the shop told me the old one had burnt wires like it was arcing. I never saw it but found that interesting. Possible it's shorting out somewhere and that's why the new one fried so quickly? Where to look...

 

Start with the connector/wires on top of the tank. May require a mirror.

 

Mine acted up a few weeks ago on a long trip. May dive into a replacement scenario which would include dropping the tank, inspecting and replacing the pump and sending unit and inspecting / replacing any wiring that needs it.