Download the service manual for your truck from the links in my signature. You can do a search in that pdf but the lamp out monitors head lights and tail lights only. If a turn signal bulb goes out then the flasher blinks faster letting you know one is out.

Have you checked the head lights, tail lights, brake lights, hazard lights?

Do you still have the hid harness with resistors connected at all?

 

Every light works. I still have the HIDs hooked up with the relay and resistors because with either the HIDs or Halogens the lamp out is still on so i would rather have HIDs. Im downloading the sevice manual and maybe ill find something

 

I just had a lamp out light on, and found that a rear turn signal bulb was the problem. The light worked but if you moved the bulb a little it would go out. Changed out the bulb, and so far so good.

 

I had a guy not too far from me that had the same issue where his Lamp Out light was on and all his lights seemed to work but he also had one bulb that was loose and causing the issue and it was one of the bulbs in the rear light assemblies.