Ok John, Stan and others, thanks for the input. I see now how the bridge rectifier would work to solve the problem. I am not real excited about taking apart some 30 controllers though to do the fix. So maybe I'll go with the bi-polar bulbs per Stan's link at 4 bucks a pop. Or maybe I'll reverse the polarity of my +16VDC supply and run with LED's on the red/green controller bulbs and live with good old incandescents on the switch machines. Hhhmmmm.....
Rod