75 Dart /6 wont start. Electrical?

Here is an important point:

HOW did you crank the engine when testing spark?

EXAMPLE:

Situation A vs B

Situation A you test spark with key "in run" and you jumper starter relay under the hood. In this case the coil is firing from the "run" circuit and "let's say" you have spark. You think "OK." On the other hand, the "run" circuit goes through the ballast resistor, which can give you a weaker spark

In this case, a problem in the "bypass" circuit (read below) results in a "no start" condtion, because there will BE NO spark when using the key to crank

Situation B

You check spark by having "your girlfriend" crank the engine using the KEY. In this case, the "run" circuit is disabled, and the "bypass" (ign2, brown) is supplying the coil. If you have a wiring or other problem in the "run" circuit, this might give you spark where it would not run, but might fire and die.

The point I'm trying to make here is you can lead yourself down a rosy but thorny path