harness plug getting hot

Just completed a few items over the winter, had the gauge cluster out and replaced the circuit boards (rallye dash) and added the LED lights. The LEDS work nicely by the way. Had to wait for a new fuel gauge voltage limiter (solid state) which was the holdup. (BTW positive we hooked up correctly-came with instructions and pic from G-Car) Anyhow, everything back together, and before we reinstalled the gauge cluster permanent we checked all the lights, directionals, hi beam ind. etc.. The fuel gauge also worked so we buttoned her up. Later this afternoon I took it out for a ride and noticed the fuel gauge was NOT working immedietly. (This SOB has been a gremlin since day 1.) I tried to play around with the ground under the dash connected to the column, checked the harness plugins (ignition harness off the column) to be sure we were still together. This is when I noticed one of the harness plugs was pretty hot while the car was running. Shut the car off, and it cools off quickly. Gauge still not working.

Just want to add the gauge had been working fine for 2 yrs. New tank-sender unit etc.. Nothing has changed there, only thing we did all winter was drop the column and pull the gauge cluster out. Any ideas why the connections get so hot?? Thinking about abandoning the factory gauge and going aftermarket if they make one for our sending units.