Brian,

I'm curious as to what you found out about your 4wd issue. I just noticed tonight that my 4wd light is not coming on... and I've never had a problem with it before.

OTOH, I've recently had the 90k service work and the rear axle seal/bearing work done and don't think I've tried 4wd since those repairs.

Could the shop have unplugged a vac line somewhere doing any of the above service work?

Where should I look?

I never did get a chance to really dig arround and resolve this issue. I'm 99% sure that my issue is electrical in nature. Heck, I've probably only driven the truck 4 times for less than 20 miles since posting this....

The other posts really helped me track it down. I did find that if I drove for a few miles, while shifting in and out of 4, it'd eventually come on. If you can get yours to come on, them it might be electrical like mine. Otherwise it's probably vacuum.

Sorry I can't be of more help, and good luck resolving the issue.

As a previous post mentioned up above somewhere, there are two wires on the front of the axle that operate the 4WD light on the dash. I made the mistake of not unplugging the connector when I did my body lift, and broke the wires. When they touched together, I got the clicking noise in the dash. I cut them off and taped them up, and don't use the wires to the light now. The 4x4 operates normally without them, since all they seem to do is operate the dash light. If you look at the axle from the front, you should see the connector just to the right of the differential. Check the connection. (If it's not that, it must be something else with the vacuum line or internal, in which case the 4x4 probably doesn't work.-can't help there).

Turns out my 4wd issue was just a burnt out bulb for the 4wd light.