Bill,
Yamaha uses a floating ground system, which can cause problems if you are using two foot pedals that have a grounded, metal frame and touch each other. This has been a problem for many years and was never addressed. Boss pedals, the type that locked together, were notorious for this problem.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)