Gonna be a tough one to find, I agree your on the right track. Could be as simple as a bared wire at a pinch point. Something to consider...I have had a rare instance where a battery had an internal short that caused issues whenever the ign switch was turned on. Only a sugestion, drop the skid plates as there are some pinch points under there where wiring passes thru. Have you added or changed anything electrical recently? Have you been thru deep water recently, you would be amazed where it gets into!