F350 trailer wiring

I have a 1999 F350 and I have found on my trailer lights (7 prong for the 5th wheel) my left turn signal and accessories go to ground. I have traced them to the cab from the plug, but do I go straight to the fuse box from here? or will they come off the stearing colum then go back?? I have got to find these shorts before I can get the trailer lights to work properly...any help???