Thank you for the advice and link to the source for the bulbs, but I need a solution before arrival of the grandkids next week.  Today I moved the leads for common or ground from U to C on the KW.  That resulted in 14 volts instead of 20 at terminal D for the fixed supply to the switches.  They operated fine and the bulbs were not nearly as bright as when the 20 (19) volts were being supplied.  However, the problem with this setup was that the variable voltage to the two trains was too low to operate them normally.
I thought about using another transformer for the switches, but could not decide where to hook the common or ground lead of the second transformer.  Would I connect it to the U terminal on the KW?
Your other suggestion to operate the switches from one of the two variable supplies might also be the answer.  Instead of operating two trains on separate loops, I can put them both on one variable supply to operate one train at a time and use the other side for the switches.  If I can't use another transformer, this will probably be the best solution for now.
Thanks again.