Funny! I was just working on my MPEMs. I didn't have any arcing sounds, but I did have one ski that had no power. It turned out that wire 1-24 (ground wire for the MPEM) on the #1 AMP connector didn't have good retention in the connector. When I would push the connector into the MPEM socket, the pin on the MPEM was pushing the wire out of the connector. I repaired that, but while I was swapping MPEMs between the two skis for troubleshooting, I pulled all the fuses. I did find one that appeared to be a good fuse, but it had intermittent continuity, so I replaced it.
I suggest you check all your fuses with a multi-meter, and check for arcing on the AMP connectors (wiring harness). Also check to make sure the bolt holding the two ground wires going to the negative battery cable is tight.
