HotRod Lincoln has nailed it...You need a diode in the
correct orientation on that exciter circuit.
Same issue I had ... Using a Painless harness and an
MSD ignition. MSD even supplies the diode in their box of goodies to alleviate the problem. I believe if you go
to their website and dig, you'll find out the value of the
diode to be used. I believe Radio Shack sells the correct ones, too.
If I get a chance to check I'll report back on the diode specs. Takes about 5 minutes to insert it and you're good to go.
mike
