Regulator issue if at 18 volts?

Big E, that ground wire is pretty short. Look just in front of the battery closer to the radiator. You should see a 3/8 bolt with something already grounded to it (turn signal ground). That is where this little ground wire goes. On the ground strap it is bolted to the back of the head and runs to one of the four bolts on the ring around the blower motor. The one closest to the motor. Check that area where the big battery cable on the negative side grounds to. It should be on the front side of the left motor mount. If this area is dirty it will play games with you on starting from time to time.
Chas.