I finally was able to ride the Sprint today to test out the changes I made. Of course, the auxiliary 10 amp fuse blowing was caused by something and that something had to be fixed. I repaired the grip heater wiring cable from switch to its next connection (pink-blue-brown wires). Ohmmeter measurements of the Carling switch revealed that the "off" position wasn't really "off" for sure. I tweaked the contact piece so that there was more clearance on switch positions (rocker forward, rocker middle, rocker aft) between the contact piece and the high/low current contact points. Today's test ride showed the grip heater hardware worked as expected. Maybe the contact piece will deform again to cause a problem. I will alert the next owner to what may be a "feature" of this switch. Before then, I will continue to monitor the grip heater performance and report back if there is a new outcome.