I am using a 100 amp (advertised) alternator, and I have minimal accessories on my bucket (Lights, horn, elec. fan). I recently installed a simple cutoff switch for my fan, since the temperature switch (third one I've purchased) in the intake manifold failed (again). So now I can turn my fan on and off with the toggle switch. Observation: when engine is running with no fan, volt gage reads about 14 volts; turning on the fan, it drops to just under 13 volts. Do I need a bigger alternator?