I would check the connections on the starter and while your down there check the starter bolts for being loose. See if you can shake the starter. See if you can get a look at the flexplate and starter gear and look for metal on the teeth. Look at the starter to make sure it isn't cracked. The wire from the starter most likely feeds some of those circuits that are not on.
Ok, wiring diagrams are here. Give me a few minutes to look them over.
http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Wiring+Diagrams&partName=TRAILER+WIRING&pageId=0900c1528025048b&partId=0900c1528025046a
Chevy Mechanic
ASE certified.