I had a weird issue on my 1993 w250 extended cab. The headlights and taillights work fine, but the hazard lights, signal lights, brake lights, and reverse light don't work. The signal lights don't indicate in the cab either when there are on. Here's the strange part: When the hazards are pushed in everything works fine, except the hazards. The signal lights signal outside and in the cab, and the brake, and reverse lights all work fine. This only happens when the hazards are on. What the heck is going on?

Also i checked the flasher and fuses and it's not a problem.

 

I had the same type of issue when I did my body swap on my 1990 Frame and dash in my 1977 body. Mine was a bad ground on the head light circuit. My left head light wasn't getting a good enough ground, so my signals wouldn't work. It may be a long shot but it's worth a look in my opinion