I put a new sennding unit in, same problem, idi pull the lead off the temp sending unit it shows cold, if i put it on it shows hot, regardless of engine tempt.

gas sending unit supposedly replaced by mechanic I got the tracker from, was not connected, I plugged it in but stilll shows empty i think... Any words of wisdom?  What is the sending unit resistance supposed to read? 

previous owner was a young lad, had underbody lights hooked up, rear bench butchered for subwoofers, aux power outlets and a load of other gadgets hooked up, probably tied something into the wrong wire - I could power my readio from the fuel gauge for all I know