I recently had some arc welding work done on my '64 F100 truck. I do have a battery disconnect switch, and according to the shop guy they did leave the switch open while welding on the frame.

Nevertheless the Pertronix module was fried. The problem was fairly easy to troubleshoot by following these steps.

1. Engine won't start, check for spark.
2. Verified no spark on one cylinder. Check for spark atop the coil.
3. No spark from the coil. Verify 12 v pulse from the pertronix module.
4. I flipped the magnet wheel upside down and spun it slowly past the pertronix module. I didn't see any 12v pulse coming out.

5. Replaced the pertronix module. Engine starts fine.

The tech support guy at Pertronix agreed the arc welding probably caused the problem. I've had the module for 2.5 years, but they still gave me half off on the purchase of a new one !! They suggested to disconnect both wires from the Pertronix module during arc welding.

Also the guy connected the ground clamp on a pretty rusty section of the frame near the front, but the welding was on the rear. This probably contributed to the problem.

 

It was nice of them to give you half off on a new module, but I'll bet they STILL made a profit on it!