Voltage regulator is mounred on rubber PALNUTS, but there is a ground strap from a bolt to the rad support.
Yes, clock and radio will drain also. Horn relay on firewall has a buss bar. One wire from battery to buss, the other wire goes into the firewall for rest of car.
Inside under dash drvr side, wire harness comes into cab, there is a crimp of two red (10 GA) wires One goes to firewall connection, one goes to light switch, and third goes to ignition switch from the crimp.
Dome light? Look behind the junction block by battery, (10 GA), I found rust between the back side of block and rad support.