How hard to gain access to the gauge?? I'll tell ya what "I" would do is run a separate wire thru the firewall and connect to the gauge. Cheaper than a new gauge. If that doesn't work, I'd get a new sender (cheaper), but I don't really think it's a sender issue. I'm ASSUMING you're getting NO reading on the gauge. A sender that's going bad will give a bad reading, but noat a NO reading. That's usually a burned up gauge.