It's either 2 ohms, 8 ohms, or 32 ohms.
My money's on 8 ohms but it's your amp's health at stake, not mine!
Seriously though, if it's factory wired it almost has to be an 8 ohm cab. 2 ohms or 32 ohms wouldn't be very practical unless it was used in some kind of custom multi cabinet rig in its previous life.