Hi guys, I was idling longer than usual the other day about 45 min. When I got back in the truck I noticed the a/c hotter than usual and my tach dancing between 0 and 750 with brief periods of all my interior dash lights coming on like if my truck had turned off; while all this was happening inside my truck was idling normal like if nothing was happening. Once I start rolling the a/c comes back to normal and my tach stops dancing. Now it's happens all the time when I’m idling; please help..

 

Check the crank sensor and its wiring.