Hate to revive this old thread, but I am very confused at the moment with my Montero and this seemed similar to my problem. I have a 1998 Montero with an aftermarket Kenwood head unit that the previous owner installed. I recently installed 2 new front speakers (
https://www.crutchfield.com/p_1131666S/Kenwood-KFC-1666S.html) and they sound great. Haven't had time to do the rears yet, so they're still stock.
Anyway, had my first long drive in the montero this past weekend and after driving for 2 hours, the speakers stopped working. The head unit was operating normally, just no sound. I tried restarting the head unit and the car, but no luck. Later that night, after I arrived and the car had sat for a while, the speakers worked again. This happened again on my drive home after about 2 hours of driving. No sound at all. I know very little about why this is happening. Would love any help!
Thanks,
Spencer