How to Repair a Couple of Wiring Harness Problems
Start by reading this article. These have been known problems for years and in fact Ma herself knew it, because the optional 60A alternators had what is known as "fleet wiring."
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
Your 3 terminal connector I believe is for the dimmer switch. Start by reading this:
http://www.madelectrical.com/electricaltech/brighter-headlights.shtml
and looking for "Crackedback" on here, who has come up with a great little headlight relay kit
Also, you can get the replacement terminals for the connectors at NAPA. I can never remember what they are called