I recently bought a used Carvin G412 280 watt cabinet, and am having trouble figuring out the correct way to connect it to my amp head. I couldn't get my own photo to upload, but this is the exact same model as mine. The only difference is, mine has this coin sized and shaped rubber insert where the empty hole is in the picture. The arrows pointing up and down seem ike they're telling you to select between setting the cabinet to 8 ohms or 4 ohms, but the rubber circle just turns endlessly in either direction, and it doesn't seem like it's supposed to come out or really do anything at all. I'm just trying to run it mono at 8 ohms, but I don't want to connect it to my amp head if the cabinet is set at a different impedance. Do I simply just run the speaker cable from the amp heads 1x8 ohm jack to the mono left input and no actual switching is required?