Alternator or voltage regulator?

[ronis <ronis@domain.elided>]

Why do my lights surge from bright to low in my Scout II? Also, the guage
inside surges as well (the needle). At low RPM's this does not occur. But
at highway speeds, it happens. The surge is very regular - with the lights
off (in daytime) the dash guage surges every 3 seconds, like clockwork.
With the lights on (at night) the surge in power is every 1 second. 

Is this my voltage regulator? My alternator is a new unit, about 2 weeks
old. What could this  be?

Thanks,

ronis