Remote start for 1966 Mustang

I have a 1966 Mustang (1965 wiring if that helps), bought a BMW Nitro 2-way alarm for it. I am having trouble with the remote start. When I try to start it, it doesn't stop cranking over, even when the engine has started.  

The wiring diagram says to connect it to alternator (positive when engine is on), I tried but I'm not sure which wire on the alternator ( i have damaged too many to risk guessing).

The other alternative is that I know it needs a 12V to shut off the start, so a 12V power when the engine is on would do the trick. But what is there on an OLD engine/car that does this? I have a mechanical fuel pump, carburetted engine, practically nothing that does that!

Please help anyone!!

Heh heh. My 'stang is far from stock! So it is a total restomod, and one of the few "hot sixes" out there! I'm not overly eager to get the remote start, it came with the alarm and I thought it would be kind of novel! But if you have seen the instructions for the alarm you would understand my distress. They are at: https://www.the12volt.com/installbay/forum_posts.asp?tid=51742&KW=nitro

I live in AZ, so no it is never winter here. But for the summer it can help to cool the car down. I have aftermarket air conditioning by classic air. What do you mean by 1-6 volt AC from the coil? I read somewhere on this forum that it doesn't work with the tacho wire.