TR-3T6 was an interesting light once resistor modded back in the day.
Came in two cell and 3 cell models.
This thread from way back may be helpful.
It’s a long thread but I think you will find all the information you need to help get a pair of your lights back up and running much brighter than stock.
Pour yourself a large mug of coffee before settling in to scan through the entire thread. It will take a while but it is worth it.
I still use my modded 2 cell version around the house from time to time.