Petronix Electronic Ignition Any Good?

What you need to do for MAXIMUM voltage to the ign system: whatever wire are providing the 12v [+] to your existing ign system, use that wire to trigger a 12 relay, the relay coil terminal.
Connect the relay
contact to either the battery [+] terminal or large terminal on the alt, which ever is more convenient. The other relay contact goes to the ign system, remaining relay coil wire is grounded.
I doubt this problem is a low voltage problem, but at least with a relay you have eliminated one possible cause.