Newell Gurus

Chester, Ozarkguy is correct. On mine the unknown switch is for seat heat. I know I have hit it a couple of times by mistake when it was 95 degrees outside. Takes awhile for the seat to cool off.
Also if you have not noticed there is a speaker in the head rest for the CB.

If you start looking for parts for this seat, you may run into the dead end that I did. I eventually just plumbed air to the seat spring via a pneumatic paddle switch and bypassed the fancy pneumatic level control.

However, in my search I did find a couple of the "brain" boxes that a surplus dealer in Canada had. I still have them if anyone ever needs them.