My TT has side marker lights but I would like them to operate as a turn signal when I turn on my turn signals such as when I change lanes.  I do not have access to the wires as they are enclosed within the body of the camper…Any one do this mod to their RV?

 I would consider back feeding the signal from the rear of your unit. I did this with mine as there is easy access to the rear lights and just ran the correct wire back along the frame and drilled a 1/2 in hole in the underbody and was able to fish a wire down  to pull the new wire up to the new fixture which I got from PPL in Texas. You already have the ground and running light power so you only need the turn signal wire. Consider a led fixture, you will love it.

 Hacker