the hubs that are outside on the axle physically lock so the truck can go into 4wd. i cant explain it technically but if they are unlocked the truck wont engage 4wd. when locked, the truck will go into 4wd. since you said switch inside i assume you have an electric/auto transfer case. this is just a electronic switch that puts the transfer case in 2hi 4hi or 4low. run the hubs unlocked in 2 hi, and if you need 4wd you have to stop get out and lock the hubs then put the switch in 4hi. if you need 4 low. the transmission needs to go in neutral before switching back and forth between 4low.
If you've got the dash switch, you don't have to get out of the truck... if everything's working right. Your hubs should say AUTO>LOCK. When they're in AUTO, they're operated by vacuum; hubs pull in along with T-case when you shift to 4hi. If you ever lose vacuum to the hubs, you can manually lock them in by turning hubs to LOCK :doh:
Some guys have problems with the shift-on-the-fly hubs and will swap them out to manual hubs. FWIW, mine are fine with over 70k (knock wood)
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