In reply to alfadriver :
They sent a whole new gauge, wiring harness, and sensor. The sensors all say Bosch on them and have the Bosch P/N.
Confirmed, the engine is well grounded with a fresh cable to bare metal on the engine and chassis. All battery cables and wires are less than 2 years old.
I will check continuity on the harness per your suggestion, though I suspect as I've now installed two harnesses and had the same problem, they're both probably fine. But I'll check, anyway.
I did hear back from Summit, and they're willing to take the unit back under warranty. Summit has always done right by me. If the harness check shows the harness to be OK, I'll send the whole thing back and try a different manufacturer gauge.
