If your 4x4H light isn't working when you engage the system, but it comes on when you start your truck for the lamp test, then here is a way to narrow down your issue.

1) On a dirt or snow covered road, turn the system on and see if it is engaging or not. (see if it will spin the front tires)

2) If it is engaging but the 4x4H light isn't turning on try switching to 4x4L and see if that light comes on.

3) If it does, and if your front wheels are driving then its not your transfer case shift motor.

4) Now go to the passenger side firewall and behind the battery is the vacuum solenoid for the IWE actuators, and on the front of it are two vaccum lines as well as an electrical connector above them.

5) Have someone in the truck while you are touching the solenoid, and with the truck not running have them turn the switch to 4x4H. It should click when turned on and hiss when turned off. If it doesn't then the solenoid is bad and needs to be replaced with part # 6L3Z-9E441-A as listed under TSB #06-8-15.

6) Be sure to provide this part# as well as TSB# to your dealer so the correct and updated solenoid are given to you.

7) This troubleshooting procedure is for the vacuum solenoid and finding out whether its faulty or not.

8) The vacuum solenoid is responsible for the 4x4H light not functioning if it is shorted out.

 

The 4wd high and low light has nothing to do with vacuum solenoid its a 2 wire on off solenoid. More than likely its the contacts in the transfer case shift motor which when placed in 4h or 4l sends a ground signal which is then turned into high or low position

 

Look up the TSB as mentioned above it states directly on it that the solenoid will cause the 4x4H light not to work if its faulty.