Okay, I'm officially stumped. I purchased a MFJ-1261 one mic-two radio box so I could use my Heil iCM mic on both my Icom 7100 and 7300. The 7300 uses a 8-pin barrel, just like the iCM, but the 7100 uses a modular connector. I referenced the pin outs for both radios and reconfigured the jumpers on radio B (7100) since the pin outs for the 7100 and 7300 are slightly different. The 7300 works perfect, but the 7100 changes the channel up every time I press the foot switch. I even completely disconnected the jumpers for pin 2 (freq up/down) on the 7100, but it still does it. If I plug my factory mic into the MFJ box the mic PTT works fine, and the radio operates normally (suggesting my jumpers are correct) but the foot switch still changes channels. I've triple checked my jumpers and even continuity tested them and everything appears correct. I've probably spent 4 hours fiddling with this stupid issue, so now I come to the pros. Thank you in advance for any help. Any advice would be greatly appreciated.