[Yosemite Sam]

I would start with the timing, simply because it is a definite, it's either right on, or it isn't. If the timing is good, then you can rule it out as a possible problem, and move on to something else.

Next, I would hook jumper cables from your running car/truck directly to the Starter/Generator, Pos to "A" terminal and Neg to ground. This is more or less another good or not good "test". If the engine wants to hesitate on the compression stroke, then the acr could be the problem. If the S/G seems slow or sluggish, it could be on it's way out. If it spins the engine over like crazy, then all is good and you can move on to something else without doubt.

There is a good possibility that wiring or grounds is your problem. However, the above mentioned things are fairly quick and easy to check, eliminating them as possible problems will enable you to move on to wiring and grounds with all confidence that this is where your real problem lies.