so i had an issue with the rear lights not lighting when the breaks where hit nore the lights on. i replaced the brake switch and multi switch

everything seemed to work then i noticed that my left trailer light was not lighting.

if lights are off brake lights work,signals work, flashers work
if lights are on right signal works,right brake light comes on when pressed,left does not and the signal does not work. this is for the truck and trailer together even with trailer disconected i still have the same issues. i checked plug on frame rail it had water in it as well so i fixed that and used to dieletic greese. anyone have an idea i am stumped....

 

also truck is a 07 5.4 f150 xl long bed ext cab/half cab ?