Recently the radio in my dads ex stopped working. He bought a new unit and it worked for about a month, then it stopped working also. He traded it in for another one and it didn't work either. Any ideas?

Well without any more details as to what the stereo did when it stopped working I would say you would need to start with the power fuse for the radio and make sure that it has not been wired without one. If the fuse is not there then it could be frying the deck due to a short. A rig that is older could easily have a short that could cause it to damage the deck.

I believe he said he could un plug it and plug it back in and it would work a while and then stop. he thinks it has something to do with the factory amp.

Ok, he says that when he turns the radio on, it plays for about 10 seconds and then makes a pop and stops working.

Did the first one do the exact same thing? The second one sounds like the power amp chip is going out or a heatsink issue on the chip.

all three so far are doing the same thing. the first one quit, so he bought a new one. It worked about a month and then started doing the poping thing. he returned that one and got an identical one and it does the same.

Hmmm, sure sounds like a voltage supply issue to me then. Those mosfet chips in all stereo's are very sensitive to voltage spikes. I had a bad altenator fry one once before. You may try to see if a shop somewhere will plug it into one of there battery/charging system computers and see if the votages are within spec.

well he works at ford, so with time He will either figure this out, or take it in.
I'm just trying to help out a little.

Ah, I like him already :)