automatic downshift when headlights turned on

I hadn't driven it in several weeks. When on the freeway early afternoon, going 65 up a mild grade, for safety I decided turn on the headlights. When I turned on the lights the engine down shifted and increased RPM's. Puzzled, I turned the lights off and the truck went back into previous gear/RPM. I tested it several times and learned that I did not even have to turn on the headlight; even just turning on the running lights caused the truck to downshift into a higher RPM. On me way home later that evening, while sitting in the parking lot, the engine did not rev up when I turned on the lights. Puzzled!

Any ideas what the heck was going on? Short? what to what? Truck does have a special towing mode. Towing mode is initiated by pressing the green button on the front dash. Could this tow mode have been shorted/switched by way of crossed wiring? shorting? could a change of current flow change the data feed to the mother board?

2002 Toyota Tacoma prerunner 2.7 liter; automatic transmission; king cab

 

I’d guess it was just the increased load on the alternator putting increased load on the engine, while sitting right near the shift point

 

Wow! I agree with your analysis. Thank you!

 

Good call. Maybe some AC compressor in the mix as well.