seperate the bulkhead & ground that wire in the rear bulkhead half & see if the gauge swings over. www.mymopar.com will have the schematics/colors for you. EDIT no go there? then go further upstream to the round connector on the printed circuit (The dash (likely) needs to come out to access that area) & there might also be an open on the power in feed side of the gauge in the printed circuit. I'd ohm the pins for continuity & be carefull pulling the round connector off of the pins (back it off/out evenly). Holler what you find. MORE EDIT Ohming will tell you if the gauge itself is dead & the more I think about this the more I think that the erratic behaviour symptoms would likely have to be the gauge or the sender, much more likely the gauge (like a tach that acts up the same way) and we confirmed the sender is OK