electrical problem with 05 t2000

Ok.. while hooking up the power to a bypass oil filter system on my 05' kenworth t2000 with a cat c15 my buddy connected the power wire to the alternater post that goes directly to the batteries without disconecting the batteries,he sparked it and my truck has been dead in the water since. no cab lights, no power to the starter, ignition switch or alternater. It is as if the truck has no batteries. I took the batteries to be tested and they are good, I have looked at every fuse and replaced the the one that seemed relevant just to be safe..nothing! I found a batteriey cable worn through close to the starter about a 1/2 in of copper showing I touched that spot with my test light and nothing. I dont know what to do next. It seems that somewere between the starter and the batteries is the problem but I dont really know..help!