Ohms for a 412 cabinet

I have a 130HD head running into a 412 cabinet. I have set to the head to 4 Ohlms. Is this correct? I presume the cabinet is wired in parallel, and if I was to add another cabinet, I would switch to 8 ohms.
Read several useful posts on this topic, but could not find the 412 cabinet option discussed.
Also, the 412 cab has a second input jack. I assume this is to connect a further cab, which if I'm correct would enable the head to power up to four 412 cabs.
Thanks,
John

The 412GS (and 412B) cab is 8 ohms. The four 8 ohm speakers are wired in series-parallel. The second jack is there to parallel two such cabs to make 4 ohms. Your amp is not going to get damaged if you run the switch at 4 ohms, but you will not get the maximum power out of it.
FWIW I used to run a 412GS in series with an RH-212 which equals 12 ohms. That was powered by a 130HD reverb head set to 8 ohms total load. I never thought I had too little power. In fact, my bandmates thought I had waaaaay too much
so they preferred I used the 112-65 combo instead.
Sincerely
Lars Verholt

John. Are the cabs you are running MM or some other brand? Like Vars says, GS cabs are 8 but EVERYBODY is different. The jacks on the CSB are in parallel so if you use two cabs daisy chained to gether and they ARE 4 ohms, that would be 2 ohms. Two 8 ohm cabs daisy chained makes 4 ohms. THe extension jack on the head itself SHOULD say that it is in series. Use those and two 4's makes 8 ohms and two 8's makes 16. Confused yet!