Giles,
What post #6 said. Pertronix Ignitors are best left on the shelf.....at Pertronix.
Use a GM 4 pin module. First check your dist p/up coil. Resistance should be 150-400 ohms. Air gap 0.006-8". If these check out, extremely unlikely that the dist is at fault. GM module has these markings: g, w [ pick up connections ] & b,c. The black p/up wire connects to terminal g. The other wire goes to terminal w.
Full 12v supply goes to terminal b, & 12v also goes to coil [+] terminal, sometimes marked 'Bat'. The c terminal goes to coil [-] & tacho also connects here. You need to mount the module on a heat sink, a piece of scrap alum 3/16 - 1/4" thick is fine, about 3 square inches [ 3 by 3 ]. Try & mount in a cool place, I have mine under the dash but can be in the engine bay. Use heat sink compound [ NOT dielectric grease ] between module & HS. The ferrules on the module are the ground return so make sure the HS is properly earthed. No problem extending the p/up wires, they can be thin wire, but twist together, keep near metal & away from HT leads or coil [-] wire.
