Have you been experiencing the engine being sluggish to turn over as that is a surefire sign of a doggy earth?
Simple to rectify.
Search and you will find a heavy earth cable connected between the battery -VE and the chassis plus one between the chassis and the engine / gearbox. Make sure that the connections are clean & tight (undo, clean, grease and tighten) and see if that makes any difference.
Although making sure your earth connections are good is never a waste of time you can carry out a simple check that will take no more than a couple of minutes. Just connect a temporary length of wire between the battery -VE (or another known good earth point) and the engine block.
If this fails to rectify the problem then it can only be damage to the harness, if you identify the connections you can then run a separate wire between them eliminating the potentially damaged wire in the harness.