Make sure the leads that run from the box to the distributer are isolated away from everything else electrical. I have had all sorts of hell with the MSD but after rerouting that connection and putting it in it's own insulation all my problems went away. I even went back to 2 boxes I had deemed bad and they worked with no problems. Personally I will never buy MSD again but will use what I have now that it's working ok. On a trip to superlift park when going to unload off the trailer it wouldn't start, determined it wasn't firing, went through the troubleshooting methods that MSD suggest, found nothing wrong, plugged everything up, fired right up and ran all day. That's what sucks, it breaks and then fixes itself without having any idea what was wrong. Have had this same type crap happen numerous times. The MSD tech told me that the box is getting confused because it's picking up signals that it shouldn't, the reason for isolating it. I look at other rigs and the same lead is bundled with other wires and it runs fine....who knows, I just know I have had my fill of MSD.