You should disconnect the battery when you change out the regulator as you could fry it - been there, done that. Make sure your ground connections are clean. Since the frame/body is your ground, make sure the body area under regulator is clean, the engine is grounded to the firewall and the battery ground (both terminal post and engine connection) are clean. Check belt tension, loose or worn belts will slip on the altinator and not give you full juice.