when i turn on the running lights or my headlights only one of the three lights turn on. the turn signal lights work normally with the signal but not with the headlights. i dont know if its in the wiring or a worn out switch.

 

Did this problem just occur? What Are these 3 lights, what year is the truck?

 

its a 92 and has done this since i bought it a year ago

 

I would start by checking the bulbs....

 

i checked the bulbs when i replaced the headlight lenses and they're both good and the signals work

 

The signals are a separate filament. Whether they work has no bearing on whether the parking lights work.

It's not the switch. All the parking lights / taillights are fed from the same set of contacts on the switch.

Did you check the small upper side marker light bulbs (IIRC they're 168/194 peanut bulbs)?

Do the taillights work?

 

Did you check and see if you have Power AND a ground to the running lights in question?