The wet and dry usually does denote a switch that completely killed the steering axle brakes. A Bendix TW type switch, which is still commonly used, controlled a relay valve. And the switch on the dash was usually marked wet or dry.
http://www.bendixvrc.com/itemDisplay.asp?documentID=2739If you scroll down on the pdf, it lists all the plates that are available for the TW type valve.
Back then, it was thought that the steering axle tires locking up on wet or icy pavement is what caused a jack knife. However, since it has been learned that the drive axle tires locking up is what causes a vehicle to switch ends. In fact steering brake limiters or omitting steering axle brakes has been illegal since about 1989. I used to run with steering axle brakes omitted to save weight. I was forced to retrofit in 1989.
Power divider locks are usually marked in and out, but I have never owed a twin screw that didn't have air. And they all shift with a Bendix TW type toggle switch.
From the looks of the picture, it is Eatons rears because of the round banjo housings rather than the square Rockwells. It could be one of the goofy Eatons that had the interaxle driveshaft going over the top of the forward axle. They only built them a few years because the Rockwell with a throughshaft was so much more practical. I don't think the Eaton even had a power divider. I think they resembled a 4 wheel drive transfer case and was used on vocational trucks rather than over the road trucks.
