Throttle position switch insulation test failure

Hello all, new to the forum.  My '83 na is failing the insulation test when tested at the harness.  If i check the switch itself on the throttle body, it passes.   The only advise the book has from here is to "check harness" (thanks book)  I've peeled back a good bit of insulation to expose and follow the wire, looking for trouble, but can't seem to find anything obvious.   Any advise or thoughts on this matter much appreciated.