Thank you kindly for the assistance.
Thanks for pointing out the Volt meter from Hall George, I ordered one while I sort out where to find a new amp gauge to keep in parts box for originality. It's interesting that my father's 1972 GTS never had any electrical problems, he owned it from new for 30+ years before parting with it. No issues on electrical parts or work for it, was eventually cosmetically and mechanically reconditioned at the factory in 1986 including the brembo brakes upgrade but no electrical needs were found or recorded in the receipts. I wonder if a shunt as described in Boss post was in place, makes complete sense! Thanks for the feedback.