i think you are hung up on this amp thing and its not the issue. if the f150 unit that was in there was working on 2 plugs then he only needs those two for this deck to work. ford has had some funky odd ball connectors, ive done tons of them and have had to go back for a new harness quite a few times. have you been pulling on the wires at all? done anything with the speakers? im wondering if one of the speaker wires has worn through causing a short on a pice of metal in the car. that would put it in a protect mode asap i would think.
its got keenwood speakers in it.