Running lites/not yellow fog lites

1st what year is the truck? Then check the fuse panel under the hood. DRL is a 15 amp fuse and it sets right next to the relay for the DRL if its not the fuse or bulbs then try replacing the relay. If your problem persists then you probably have an open wire or power problem leading to the lights.

When I first bought my (used) '02 Silverado, neither the salesman nor I could get the darn things to come on. The service dept. For the dealership explained the way they work as follows.

The DRL's will only come on when:

a) the emergency brake is off, and

b) when you shift out of "Park" into "Drive" (Or maybe it's any gear other than "Park".)

This means you can't even check them unless you've got someone in the truck who can take it out of gear and (hopefully) hold the brake pedal while you check the bulbs.

Or, just to see if one or both of them is broken, you could just pull up to a wall and see if you see a reflection from them.