cause of all lights going dim ?

[JD3426]

Bill & Hank,
I have had no luck finding the problem so far but still looking. As far as the ground in question. My '72 came with an AM radio and has never had one. Never a problem until recently, if adding the additional ground strap solves it I guess I will be happy but also wondering what I am misssing ? I did discover yesterday that the horn is not working, dont regularly use it so am unsure when that issue started or is it is related.

Thank you both for the help.

Jim