Hello, MI-Mitzu. We live in a frustrating winter.

You'll be able to edit posts once you get a few more posts under your belt.

The best I can offer is to check the wire that goes to the sending unit, and make sure it's not grounding out by way of grease or oil, or shorting out somehow. I was stumped by the pressure relief valve, too, and the book says nothing about it.

Essentially I'm just offering a sympathetic ear, and a shade-tree mechanic's view.