when i put truck in 4wheel drive the light on the conole doesn't light up and when i drive it the light will come up then turn off when i step on the brake ,the truck has auto hubs and also i notice a vacuum diapragm next to the battery tray with a rod that goes to the front axle what does that do , when i'm stuck in the snow and put it in 4wd the front wheels don't drive ,any insight will be appreciated ,
thanks andrew
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