Don't know if this has anything to do with your issue but i am putting this out there because when i did work at TKE we ran across this on the TAC20 and the TAC50's....check all your connections that are factory installed, we had an issue in are area were the wire was behind the screw termainal! didn't start having problems untill almost a year after install. found this on power supplies and "aux" relays to the starter.
