turn headlights on, rpm's increase, reverse light on

My father has a 2000 4runner with drl. When he turns on the headlights , the truck's rpms increase and sounds like it's dropped a gear or something. Also the reverse light will lighty appear on the dash. Sometimes the truck will through a p1780 code which was the park / neutral switch.

We've replaced the p/n switch, swapped out instrument clusters, checked all exterior bulbs and connections but no luck. Just a few days ago, I noticed the headlight bulb was bad so we replaced it and tried the truck again and thought everything was fine. Next day, problem is back and the stupid p1780 code is on again.


Any suggestions? What could be screwing the electrical up? Could it be a bad drl relay, headlight switch, or what?

 

How much do the RPMs increase? A 100, 200?

When there is an added amp draw on the alt, turning on fogs for example, it adds load to the engine which the ECU can sense and increase RPMs to compensate. I've seen this happen on my truck.

 

rpm's go up and up very quickly until we stop it. It's always a few thousand before we stop it from being afraid of ruining the transmission.

 

Have you tried asking over at YotaTech? That's where the 4Runner gurus are ...