My friends 74 Challenger has the same part in about the same location. We've been trying figure out what its for too. He has purchased a new wiring harness for the year and month, but no cable for that module. I hope someone can help.
Keeps us informed on the progress. I may be able to help with parts ID as I have a 67 FB that I purchased in parts as well. Its a load of fun trying to work things out, and the added bonus is, you dont have to pull it apart.