What does this wire do?

Hey everybody. I've searched the forums and read some good info on motorola alternators. I just got a new alternator but its not charging the battery. The "yellow" wire that comes from the external voltage regulator is supposed to go to the ignition terminal on the solenoid (so I've read). What does this wire do? It isn't hooked up right now. And I have an HEI distributor and the only wire I have running to it is from the ignition switch not to solenoid. How should I hook this up?

 

I put a week into trying to figure out that regulator. Wouldn't put another 10 minutes into it. A standard delco remy 10si alternator works just as good, installs much easier, and in my opinion is more reliable. Only 40 bucks

 

Thanks for the tip, I heard a lot of people like that swap. I used to work at a mom and pops auto store (still do a little during school semester) and I called the alternator guy in NY and asked him. I guess I was missing the wire from the ign switch to the regulator, so it wasn't getting power. Bought a new regulator for the heck of it, wired it up, and she charges!!!R) Probably do the Delco when this one goes.