Well, not exactly a 5.0 Mustang question, it is a 5.0L 1986 F150 question. My truck has another problem, seems there is another problem every time I go to use it anymore. Recently, I ran codes on the truck as it was not running right and got several--one was "no tach signal" and the other was "temp sensor voltage out of range". I have changed the thermostat, changed the temp sending unit, wiggled wires, cussed, and everything I can think of. The guage no longer rises into the normal range even on a hot day with the A/C on. Now--a possible cause, I recently converted the instrument cluster from a non-tach cluster to a factory tach cluster. I used the tach and printed circuit board for the tach, swapped the speedo because the new one had a trip odometer, but left the other guages in place. It was after this that the problem seemed to appear. The truck doesn't seem to run hot and the tach works. I am not worried too much about the code "lack of tach signal" but the temp code and guage problem are really bothering me. Just some other info--this is a speed density EFI with EEC-IV. Any thoughts?