_Usually_ the primary, or one of the primaries, begins at pin 1. If
you get two windings that measure about the same resistance, and its a
few ohms, it's probably a split primary. You can insure that you get
the phasing right if you connect the two windings in series, and apply
120V to just one of the two. Then if you get about zero volts across
the whole series connection, you have the two connected counter-phase,
like dotted ends connected together. Try the other polarity for one
winding and see if you get 2* the applied voltage across the whole
series connected primary, which would be in phase (dotted end of one to
the undotted end of the other.

It's helpful if you have a variac (NOT a lamp-dimmer triac) so you can
run the voltage up slowly. An alternative that works nicely is an
incandescent light bulb in series with the 120V supply. If the series
lamp, 100 watts or so, lights very dimly or not visibly at all, with
nearly all the voltage across the transformer winding, you've almost
certainly got it connected to the primary. The light bulb will keep
you from blowing breakers or fuses. If the transformer has an internal
short or you're hooked to the secondary (or if you short the secondary
or put a heavy load on it), the lamp will light much more brightly.

Of course, be careful. The primary side can give painful shocks,
possibly leathal ones. And the secondary side can deliver enough
current to make pieces of metal very hot.

Cheers,
Tom