likely you have a shorted switch. its a replacement item, and the cost is roughly 43 dollars from mitsu. there are 2 left in the u.s. in atlanta warehouse, so i have been told by my mitsu parts help.
my light is on all of the time.
that little pest is a lot less troublesome than trying to change the sending unit.
its in a very easy place to reach if you have eyes in your fingers, a grip like a gorilla, and tenacity of a wolverine.
having none of those traits, i just leave the light on.
soon when the rain subsides a bit (july), i have a number of chores to do under the truck in that area, and i will remove the wires and short/unshort them to extinguish the idiot light.
if you are concerned about trans temp, (you should be), you can install an inline temp sender with dash gage.
i had a 26K flat plate oil cooler . i used that to cool the transmission fluid.
my old trans cooler is now my power steer fluid cooler.
so... if you dont want to build a bigger cooler so you know for sure your fluid is cool, then an inline or even pan sensor is the ticket.
do the normal check on your fluid if its healthy then its your sensor acting up.
its possible , it has happened, that u may truly be overheating, do all the usual checks b4 listening to my balony.
