I assume you're talking about the Scout cab. There should be a sticker located near the tweeter control. If it's gone, then a call to Mesa with the serial number of the cab should get you an answer.
The WA amp itself is capable of 2, 4, or 8 ohm operation.
I'll check with Mesa today...thanks!
Can't you just unplug the cable from the amp and slap an ohmmeter across the plug? If the speaker has an 8 ohm voicecoil you'll measure a resistance of something just under 8 ohms, if it has a 4 ohm voicecoil you'll measure something just under 4 ohms.
The crossover (etc.) for the tweeter won't come into play as the crossover capacitor blocks DC (which is what an ohmmeter uses for measurement purposes) making the tweeter invisible to the ohmmeter.
Thanks! Come to think of it..I do have an ohmmeter...forgot I had one!