1990 W150 when the driving lights are on, the right front side marker light is dim and the right turn indicator is on solid in the dash. When I turn the right turn signal on the right side blinker outside and in the dash blink normally. I guessing it's a bad ground somewhere but I can not find it. Am on the right track or should I look at something else.

 

you could try running a piece of wire from the negative terminal on the battery to the ground on the light. if this does not help i would checking the ground on the other lights. could also be that someone replaced one of the marker light sockets and re wired it wrong. i know i did and had the exact same problem.