My 4 wheel drive stopped working. When i press hi and lo no lights even flash. I remember reading something a while back about if you have problems with where the air/heat comes out of the dash then that could be related to the problem? and i have issues with that right now too. Any suggestions?

 

If you have no lights on the switch, then the problem could be fuses or another electrical issue (corrosion, bad wiring, etc). A vacuum problem shouldn't cause the lights to go out, it would just prohibit the engagement of the front axle.