Regulator issue if at 18 volts?

Always best to check the simpler(and cheaper) things first. Especially since I'm after electronic ignition soon. I'll confirm that my ground is good at the firewall for my regulator and make sure that it is actually the regulator. I know that my only ground at this point coming off the battery is to the engine block!!! There is another black wire coming from the battery to the inner fender for body grounding but it is broken completely off!!!! I will fix this first. SHould there be a ground strap on a slant 6 from the engine to the firewall for more chassis grounding in 1970??? I see that the starter is only grounded through the engine black, an amazingly simple engine and electrical setup.

Thanks.

Ernie