I have a 1999 Chevy which is stuck in 4x4

check and test module and harness https://www.youtube.com/watch?v=i04AE6r6YLM

It could be a junk switch or it could be bad contacts inside the transfer case motor.. Does the transfer case switch to the selected gears? Everytime? If so, you might try another switch. If it does the same, I would say the motor contacts are bad. Replace the motor if you want the lights, But I personally wouldn't do it until the motor quit switching gears. They're not cheap.

You replaced everything. The only thing left to fix would be the wiring. Check for power and grounds first. then start replacing the wires.

vacume problem for sure

have you checked the transfer case motor

That depends a lot on how your truck is equipped. GM uses several different 4 wheel systems including AWD, Part-Time 4WD, Full-Time 4WD, and ON-Demand AWD. Then there is another version used on some trucks that is a combination of 4WD and On Demand AWD. - it gets a little confusing but each system as slightly different charachteristics.

Genericly speaking, if you have the push-buttons on your dash that say "4-HI", "4-LO", and "2HI" and/or Auto-4WD , the transfer case has an electronicly-controlled stepper motor which shifts the transfer case into the selected mode. An electric solenoid/actuator then engages/disengages the front differential for 2-Wheel or 4-Wheel modes. One push of the button and it shifts the transfer case and engages the front differential.

That's much easier than the old days when you had to stop the truck, get out (Sometimes in the middle of a big mud hole) and lock the front hubs then get back in and play with the lever in the floor to get the transfer case to shift into the desired mode.

The 4x4 switch on the dash likes to take a dump in those years. They also like to eat encoder motors. If you have a way of checking it, try and get the codes out of the transfer case modual. b2725 means you need a new 4x4 switch on the dash. c0327 means you need a new encoder motor. There are a bunch of other codes that can be in there. But I'll take a guess and say those will be the ones you'll see.

Oh and for what it's worth the encoder motor is the the thing on the transfer case that shifts it. It's a electric motor. And it's NOT cheap! So make sure you find out if it's really bad before you put one in.

If it has the push button 4wd selector on the dash, it is most likely the transfer case encoder motor. Not to bad to replace but you will have to remove the front driveshaft.

Replace the push button selector assembly. Common failures. If that isnt the problem then the encoder motor on transfer case has failed. Try switch first.

i have a 1993 blazer 4.3 w code 4x4 with a 4L60 E . my truck wouldn;t go in 4 hi or low. so i changed the transfer case motor and it works fine now. If you turn the ignition key to on but not crank the engine and open the driver door and push 4 hi button, you should hear the transfer case motor cycle for 3 or 4 seconds every time you push button and the light will flash until it goes in 4wd If the 4 hi button light doesn't flash during cycle then it could be a bad switch. if the transfer case motor won't cycle it could be a fuse or a bad transfer case motor . Hope this answers your question.
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