Where are you hooking the line to the carb? If it dies when you hook it up, then it sounds like you're hooking it to the wrong port. The correct port will have little or no vacuum signal to it while idling, so should not effect your timing in the least.
Try another port.
Why is timing it with a light a problem? Don't be vague, give it to us straight. We can take it!
What is it doing? Are the timing marks not lining up? If so, maybe you've got the wrong pointer for your damper? Too many combinations, so it's very easy to get the wrong one.
Don't know if you need to call the cam manufacturer, since you have determined that the firing order is correct for a 351, you should be good to go there.
You just need to verify where you timing really is, so you can know what to do next. And you need to be able to follow the advance curve too, so you can determine what, if anything, is amiss with your timing.
2 wires for the alternator is fine. The large black one is for charging, and the Orange one is the Field wire that runs straight to the voltage regulator's "F" connector.
If still using the original Bronco harness, your ground wire (fairly important!) is molded into the strain-relief as the little attachment ring. It connects to one of the "GRD" posts on the back of the alternator and the other end (small Black w/red wire) goes to one of the mounting bolts of the voltage regulator.
Not sure what a Yellow wire is doing there. Only two common ones under the hood that I can remember. One is for a horn relay (if so equipped) and the other is for the voltage regulator's "A" connector.
That one should be connected directly to the large Black wire, but does not usually run anywhere near the alternator I don't think. Hmmm, I wonder if it's normally molded into the strain relief and would be exposed if the wiring harness were pulled apart.
I thought I remembered it being on the battery side of the harness, but maybe it's in the alternator side after all. Not sure, but it doesn't normally hook to the alternator itself.
Follow it up into the harness and see if it goes to the regulator. That'll tell you what you need to do with it.
Paul