4 wheel drive service light is on, wont engage into 4 wheel drive and the indicator lights wont come on, what do i do?

On the full size, the front actuator is electric, not vacuum.

When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.

Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.

I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.

GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.

If I were you, I would buy a new heated actuator. They are available at most auto parts stores, and are about $90. They are also on eBay for about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.

Good luck, That actuator is usually the problem 90% of time but check the fuse first in your fuse box.

4 wheel drive service light is on, won't engage into 4 wheel drive and the indicator lights won't come on, what do I do? I had the same problem, but my service light wasn't on (Key word HAD). First, I took the truck to a Chevy dealer and my jaw dropped when he said "We can look at this for ya, but not knowing what the problem is, it could be anything, and oh ya, we charge $100.00 an hour." I could not afford that. So, I did as you have done, looked on the internet to see what I could do, I did the following:

1. Looked for a blown fuse. I only found one fuse that said FWD, and it was the one on the inside the cab. Looked good. NOPE

2. Changed the selector switch. NOPE

3. Changed the actuator. NOPE

I don't work on cars, and don't want to. So, it sat all summer. Winter is coming and with the extended cab long bed truck I knew it would not be good without the FWD. So, I started again trying to see if I could fix the problem, or take it to someone that would not charge an arm and leg just too maybe help. And long an be hold there is a fuse. It's not labeled FWD, its labeled ATC. (Automatic Transfer Cass) It's under the hood with all the other fuses. So, I don't know what the actual problem was or how the fuse got blown, all I know is its working, I just had to try them all, I guess. Good Luck!!! And thanks everyone that posted on here. IT WORKED. I don't one which one did it, and don't care. I got My FWD back.