Running board light drivers Side not working.

Check wiring at the headlamp connection. There something loose.

fuse for each side of the lights including the dipped light ,most likely a 10 amp(red) look in the fuse cover of handbook for what fuse its what

probably corrosion on the ground wire to the bulbs or the wire to the bulb did he check from chassis to connector or just take the bulb out sounds like you need to find a real mechanic

do you have power and ground to the bulb socket knowing what side is bad will help find the problem

If it is a tail light and only one side is out, it could be the socket the bulb goes into.

Check for power with a test light(not a dvom) at the tail lamp assembly. Test right at the spot where the bulb socket sits. If you have power then i would check the connection tab on the bulb socket itself for pits or corroded tabs. If you do not have power present at test point then double check the fuse chart and see if it says 'electronic' instead of having a fuse amp rating for the tail lamps. If it says electronic for any of the light circuits then it means their is no external fuse that can be replaced and the problem is most likely internal of the headlight switch. Since the headlight switch is actually a power source for the lights. I would start there at this point. Let me know what you find and if you need anything else just let me know

General Motors did their best to confuse us shadetree mechanics! There are three locations to check. One is the passenger side fuse panel. Next is a large panel on the top of the drivers side fender under the hood. Lastly, just inside drivers door on the end of the dash. Normally the cover is somewhat triangular shaped.
Good luck!

you probably got the wrong bulb
those are usualy a different number higher wattage, they look exactly like an 1127 but are a 2027 or even a 3027 check the bulb base it has the number printed on it

I have a 2001 Ford F150, my brake lights dont work. Ive replaced the bulbs, checked the fuses,and the brake switch on side of the brake pedal was replaced. I still dont have any brake lights. My third brake light works fine, along with my running lights,flashers, blinkers.

you need to check and see if there is power to the light that is out , because they work on the same circut , look for a bad wire ?