When I worked on a route and had a problem with frame rails causing "tickling" between two machines; it was always* a broken 3rd prong. If I wasn't carrying a replacement plug end, I always had a spool of 16 or 18 gauge wire. You would cut off a 12' piece and attach it to the ground braid in the backbox, route it through a rear vent hole and into the machine next to it. Connect that end to the ground braid. Problem solved temporarily until you could follow up in a few days with a new plug end or cord. The length allowed movement of one machine for service.

Keep in mind this was before the days of Home Depot, Lowe's, Heckinger and Builder's Square so you couldn't simply drive a few miles and get one. Hardware stores, which closed early, were your only choice. The only "superstore" for building materials was Forest City that became Handy Andy but bankrupted thanks to Home Depot/Lowes.

*: One time, and only one time someone had removed the nut holding the ground braid to the side rail bolt on a Bally pin. All I had to do was reconnect it.

Thus, to troubleshoot; take a jumper wire to one rail and then to the rail on the pin next to it. If touching both together cures the shocking sensation, figure out the disconnect. If instead a spark/explosion takes place and the circuit breaker or GFCI trips, you have a bigger problem. Standard electrical troubleshooting techniques apply.