Larry,
If the alternator is a 78/79 it would be internally regulated. You would not use the regulator in the firewall. Look at the plug that plugs into the alt., if the plug looks like this (--) it is an internal regulator. If it looks like this (II) it is an older model and would use an external regulator. Why not just take it off and get it checked, most parts places check for free. It's only a couple of bolts to remove it,and if you're not smelling anything burning it's probably bad and will need to be replaced anyway.
