I have a 2001 Toyota Tacoma prerunner auto v6. When the lights are on the left turn signal stays on and it will not shift out of low. When the lights are off everything functions as normal. I have a code p1780 that will trigger when I turn on the lights. I realize that is for the neutral safety switch. I have seen several post that suggest replace neutral safety switch, circuit board behind gauge cluster and removing trailer light connections. Most post claim the neutral safety switch didn't fix the problem.I have already removed the trailer light hook ups. Hoping someone else has experienced this and can point me in the right direction other than just throwing parts at the truck! I don't have that kind of money! Thanks - Michael

 

You mean, with lights on you get the error code right away?
Sounds like a short between your light circuit and the neutral safety switch circuit. Inspected our wiring?
You mean you're able to shift INTO low but not shift out of it? How about other gears?

Anyone here care to share your schematic showing above systems, as well as the shifter safety interlock solenoid, so we can see where problem might be introduced?

 

I can reset the code,drive the truck without the lights on and it will shift normal and not throw a code. When I turn the lights on it will throw the code and will not shift out of low gear while in drive. It will go into all gears fine, but if the lights are on and it is in D,2, or L it will not shift out of L. I have seen this problem posted before but have never seen a solution. I have checked all the bulbs and taillight wiring harnesses. I disconnected my Reese trailer light adapter( because I heard they could go bad and short). So far same results. Just happened 2 days ago and have traced any other wiring

 

How is your charging system??

I know these ECT computers do strange things if the voltage drops to low.

Might just be poor or corroded connections