Going crazy with new Duster and over voltage issue.

Please remember you are dealing with a 50 year old car regardless of mileage. So every connection could be dirty, and or corroded / loose.
Every item has been touched by human hands more than once…. Double check everything. Also, get a copy of the wiring diagram from that particular car. Learn to read it properly. These systems are simple when you understand how they actually work. We are all guessing to help you based on what we have experienced in our past.
A few pictures help also. Lots of people on here have keen “eagle like” eyes and can spot issues just from some well taken photos or video. Good luck.