question

@jfosdick, this is a bit of a new one to me... there's very little in the temp sensor that could possibly fail, and by all appearances you do have everything hooked up correctly. I suppose the one thing that I'd particularly suggest doing is replacing the fuse in the inline fuseholder... I haven't seen it on the temp sensor, but I've seen cases on the standard shunt PCB power supply cable where the little fuse "half-blows"... basically it's intact enough to allow some current through but not all, which ends up causing hinky little voltage drops that make the BMV readout go wonky. In your case, given that you have about 6/10 of a volt difference between the battery reading and the reading off your sensor wires, I think that maybe the sensor fuse is either not seated well in the fuseholder, is the wrong fuse, or is partially blown. Recommend putting in a new fuse (1A) and seeing if that fixes the problem... while you have the fuse out, by the way, check the insides of the fuseholder for any miniscule oxidation that may have built up inside, as I've seen that twice before and in both cases was enough to cause voltage drop, which with instruments as sensitive as the BMV and associated accessories, is enough to make them misbehave.

Good luck!

@Justin Cook So I popped it open and checked fuse contacts. They were bright and shiny. Fuse looked pristine but swapped it for another and got the same result. So then I just went rogue and joined the two fuse contacts together with an alligator clip and everything came back on exactly the same. Again lol. So not thinking it's the wire. Next simplest answer is data cable? Idk.