Unknown Brown Wire with Ring Terminal on 66 Barracuda

Awesome, thanks!

I looked over the two wiring diagrams but since the heater works OK, I didn't think it could be from the heater.

If the wire Y's then it must be getting enough ground from the other side.

I'll run it behind the passenger side kick panel and ground it and see what happens!!!!

Then like some other wise folks said put a meter on it and check it first.