Did the gauge beep at all? It has to have a clean contact, no plastic sleeve or rust. Also, keep the tip clean, wipe it with a clean cloth. You could try new batteries if you haven't already.
2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.