Well, it's no wonder they had to add a grounding wire for the horns, what with the reinforcing bracket in between that serrated bolt head and the radiator support.
So basically they ended up connecting the horn to the reinforcing bracket.
I thought only the '69 cars got the reinforcing plate. So how (relatively) common were the reinforcing plates on the '70 oil cooler cars?
Great write up! I wish it had come out a month or two ago when I was fidding with getting my horns remounted properly. Looks like I'll be going back and redoing a few relatively-minor things.