I have a 1998 f150 4.2L and I'm having problems with my running lights. If I have the truck parked and running, the running lights don't work but if I turn on my headlights they work..any suggestions? I'm thinking its just a relay but would love any advice

 

Moved to correct section

 

Are you saying the running lights only turn on when you have the park lamps/headlights switched on?

 

Daytime running lights or parking lights?

 

Check the fuses first off, if they're all good, then your daytime running light module is probably shot. When they go they will either leave the lights on at all times, or the lights won't come on at all until you hit the switch. It's located driver side, attached to the rad support right up front. It's kinda hidden behind the bumper.
Good news is it's an easy fix, just like one bolt holding it in per side (two bolts total), plus one connector to undo.
Bad news. I don't think any ford dealerships carry the part anymore, and I doubt you'll find it online. So you'll have to go to a junkyard and rip one off a junker. Also, 97-98 are interchangeable, but 99-03 are different. Make sure you get the right one.