Instrument Lights

Find the marker light relay and swap it with another one to see if it's stuck.

 

you should be able to hear the relay click on and off with the light switch. check the relay box cover. most trucks will have spares. if not swap it out with one you wont need right away.

 

Sounds like either a stuck relay or you have a short to power somewhere. Start with the easy stuff like relay swap first.

My question to you: are your tractor marker lights stuck on all the time as well or is it just dash lighting?

 

Yes, I agree. Short to power. I would start with some easy stuff. Open up the dash panels and jiggle all the wires around. Chances are the short is outside. Do the same with someone inside watching the lights. If wires go into a box on your rear light rack pull and jiggle the harness going in. Look under the hood and try them there also.