Grounding Terminal

I am not sure on a 72, but on my 73..If you are on your back, head on the floor against the brake pedal.. the ground bolt, really small. is up and to the far right. close to the side, near the firewall. you will see alot of black wires together, all going to a single term. On my car, it looked like they painted the underneath, and then put the wires on. took a bit of scraping to get the paint off. and as you probably know, you have to do all this in a space the size of a breadbox. Good Luck.