When You say that the radio sometimes works and then doesn't. What do you mean? When it doesn't, is the power to the radio shut off as well. Or, is the power to the radio still there and you are not recieving sound from the speakers?
In anycase there may be a short somewhere down the line. I would pull the unit from the dash and make sure that the red and yellow positive lines to your sterio has good connection, and check the ground connections as well.
However, if you still have power to the unit but there is no sound comming from the speakers. As with my 96 Ram 1500. I ended up replacing both the speakers and wires. If I turned up the volume past 15, the speakers would shut down. I would still have power to the unit though. It turned out there was a problem in the factory speaker wiring harness.
So I directly hooked my speakers to the system bypassing the harness that came from the fasctory and all is well for me. I used the 18 gauge speaker wires..
Hope it helps......