To close this one out...After much trial and tribulation I have figured out what was causing this problem. Low voltage at the coil. I had just 10.9 volts at the coil so I pulled the ballast resistor out and wired everything without the resistor and got 12 volts at the coil. Took it for a test drive and it runs great.

The bad news is I put in a new Mallory resistor and the voltage drops back and the truck runs like crap. I just pulled the ballast resistor and will run it that way for now. I know the Mallory installation instructions say you need the ballast resistor but I checked with their rep and he said it was ok to run it without one when your just at 12 volts on the coil.

At least I can start driving this and working other kinks out. Put my first 20 miles on it yesterday without incident. I'll still need to sort out the problem in the wiring harness.

 

Actually 10.9 volts would be high voltage at the coil, not low. It sounds more like a bad coil if the addtional voltage fixes the weak spark problem.

 

Let's make sure I'm doing this right first. I pull the distributor cap and rotor off then turn the key to on, put my volt meter on the coil's negative terminal and to ground to get the voltage going to the coil. That should be 12 volts or basically battery voltage. The ballast resistor is normally in the circuit to essentially regulate the voltage going to the coil/distributor to make sure it doesn't see a huge spike that can burn out the optical module. At least that's the way I interpreted how the Mallory rep. explained it. Does that sound right?

 

I ve had the same problem on a buds car with a diff. motor. After taking everything off the motor or pluging it up, making shure timing and all other variables where ok, i pulled the heads to find a bad bore job. A "good" engine builder had done the work.