Need help on my truck....Head lights turn on, but marker and trailer lights off....

I believe you might be low on this...

 

Are both controlled by the same switch? I've driven more recent models and it is a knob you turn clockwise, with the first position turning on the marker lights and the second position turning on the headlights. If this is the case the first thing I'd do is check the switch itself. You might have dirty contacts. Worst case replace the switch.

Also check the fuse. It could be a loose or bad fuse.

 

I'm not sure what your switch looks like but I have a 2006 Columbia and experienced the same problem. Here's a link to the thread I made on how to fix the interrupt switch. http://www.thetruckersreport.com/tr...m/238900-fix-for-marker-interrupt-switch.html

 

Great thread and good link to that Youtube video. I've found doing Google and Youtube searches for various fixes to be very helpful. Many of the Youtube videos were invaluable.

 

Thanks Lepton1. I was just trying to do "my part" when writing it with the noob in mind. A lot of times I'll read about solutions to problems on here but rarely find anything that reads like an instruction manual. I can't tell you how many times I've wished people would go into [great] detail on their fixes/explanations/mods. We're not all mechanics and not everyone knows what certain parts look like or where to find them. lol