Maybe a main relay of some sort??

my ranger had a problem just like that and it was one of the relays for the interior power..

Stupid thing to try thats how i found out what was wrong with mine.. i hooked up a straight 12v source from the battery to the Yellow wire from the radio... (all time power) not 100% what the real color wire is.. but it did work in my truck.. then i replaced the relay..