I have not worked on many of these distributors. On some old Chevy's there is a threaded machine screw that the primary feed wire connects onto the distributor that is surrounded by a piece of plastic. If that plastic got damaged then you will have a direct short to ground. There is a special tool to use so that plastic insulator does not get broken.
This may not apply to your truck. But something for you to check until others check in. Jeffrey
