Running a ground wire between the generator housing and the regulator base usually makes the regulator operation more reliable. It's a good idea on any vehicle, as otherwise the ground for the regulator control circuit has to rely on a convoluted path from the body to the frame, then back to the engine. You will probably find a wire going to the regulator base that will be the other end of the one attached to the generator housing. Check it with an ohmmeter with both ends of the wire disconnected. It should read zero ohms or very close.
Here's a generic wiring diagram from Delco for all GM generator/regulator circuits with the "A" design, where the ground for the field coils is found at the regulator. That covers virtually all GM vehicles I'm aware of.
http://www.hunt101.com/data/500/D-R_Regulator_001.jpgJerry
