[Richard]

Well, no two Newells are alike. So forgive me. Neither of mine had a solenoid like that activated by the tag switch.

   

This is my differential locking solenoid. 

Knowing how the tag axle lower/raise function works is hard to reconcile with that solenoid. Here is why. The system as used by Newell to increase or decrease pressure in the tag bags maintains right to left separation. I would just have to see how that is plumbed with ONE hose to maintain side to side separation of the systems. 

You have mentioned previously that you have found electrical wiring issues created by a PO. Is it possible that the wiring at the switch panel is flummoxed some how? You could easily confirm by decreasing pressure in the tag bags, switch on engine off, of course. If decreasing pressure in the tag bags causes the rear of the coach to squat then I am full of mud of what the solenoid you pictured does.