can I use A/C the other side of a swithch too work D/C "IF"..

Not sure I understand your description but I'll propose a scenario.  Let's say you have a 9V battery that powers a sound module with some kind of launcher audio-effect. 

Presently each button applies 12V AC to some portion of the launcher.  Since the 9V DC circuit and 12V AC circuit are isolated (not electrically connected to each other), a button can be shared.  In other words by pressing a button, only 12V AC goes to the 12V AC launcher mechanism at the same time that only the 9V DC goes to the 9V DC sound module.

Thanks for the response !!!  my  electrical house friend said I can not di this! because A/C for Lionel transformer will always s be their, He told me I have to isolate the d/c voltage ..

As pictures once wired up the center would have 12volt A/C Lionel and share a 9 volt D/C  but the grounds  never would touch!

What do you think do I have to?

Thanks again! DANiel  

As long as the two power sources and the circuitry are TOTALLY isolated from each other, you shouldn't have a problem.  I do a similar thing with a relay in some of my upgrades.

Yea that would of been a problem the way I thought it might of worked  thanks for the info! Now I have two separate switches  I cut the power strip in two drilled two holes and riveted them back on and soldered separate hot wires on both ..thanks again ! DANiel