Audio Systems: Poor AM reception, fm reception, ford ranger

Question
Hi Garry,
I have a 1989 Ford Ranger with the original factory installed AM/FM radio. FM reception is quite good but AM reception is limited to stations that are within a few miles. However, AM reception is quite good when the engine is NOT running. What do you suppose is the problem? Thank you very much!  

Answer
first off, try changing your plugs and plug wires with resistor or supression type.  (same thing, just some brands call them one or the other) if this doesn't help enough, then go to radio shack and get their noise supression kit. you might also redo the body to battery ground wire or install one if not there already.