FYI I have had problems with the universal sending units from MACs. I used one in a tank I made for a '52 3100 and when it went bad I assumed when I welded near it I burned it up. I took the bed off replaced the sender with another from Macs and it lasted a couple of months when it too went bad. I pulled the bed off last week and replaced it with a different suppliers unit.
To test I operate them with gage out of dash and sender in hand, i repeat each test as the pieces are assembled, the final piece being the gage returning into the dash. I also run a ground jumper to a screw of the sending units' flange as if the tank were plastic.
