Newdude and Another JR,
Thanks for the more technical response to my inquiry. I did not intend to confuse the question by mentioning the California DOT requirements but that was suggested only to consider the possibility that the markers may be disabled by coding or it may be simply that California does not allow the option to be sold in state.
I did not want to get into the reason I wish to do this and was intending to focus on the how, where I fully expected this to be a simple exercise of replacing the fuse and/or relay with a contact extension, with a switch in series, to allow the option to be selected when desired from inside the cab and not making any permanent modifications to the vehicle.
I do have the schematic but cannot for the life of me, find the fuse (F34UA) or the relay (KR53) under the hood so I must at this point assume I'm blind, but if anyone can take a picture of the box showing either of these devices, that would be most helpful.
Thanks to everyone for their comments and suggestions to date and I look forward to any additional feedback possible.
JT