Poor Spark?

Calipag said
We've installed the 318 from our 1974 Dart donor car in to our 1970 Dart. It was running when removed and the distributor was not removed. I cleaned up the electronic ignition and installed the GM module and Ram Truck coil.

I'm trying to start the engine after the swap and I have a strong spark from the coil wire.

I have very weak almost no spark at the plug wire.

It has a new cap and new rotor.

The engine does not want to start, and is back firing. I've checked the firing order and made sure TDC and the distributor are correct.

The Spark is the only thing that I feel could be the problem but don't understand why the spark is so weak.

Am I missing something?

On my car with the same symptoms it turned out my original firewall to block ground wire was bad. The connections at both ends were clean and tight and the wire tested good for continuity. Ground wire from battery to block was new and both connections clean and tight. Replaced firewall ground and problem solved. It drove me nuts.