[fordtough.ca]

3 things may cause this:
1) you may have melted some wires (are you blowing fuses)
2) loose or no grounding at turning lights
3) bed light connector or wrong light bulb

Most likely it will be second, its a most common problem

 

[fordtough.ca]

im curious if by the second one you mean the ground at the switch for the lights or at the actual bulbs of the lights?

thanks

Bulb of the lights
The best way to check this it to remove bulbs out one at the time,
Process of elimination
Hope this helps
Keep us posted