Dick,
I will change it around so the switch isolates the TIU from the track when running conventional.
Just remove the switch altogether. It's completely unnecessary.
To operate your DCS engines conventionally, just use the Menu command to turn off the DCS signal on all channels. Then, to later operate under DCS, use the same menu command with the AON soft key to turn the DCS signal back on.
This and a whole lot more is all in “The DCS Companion 3rd Edition", available for purchase from many fine OGR advertisers and forum sponsors, or as an eBook or a printed book.