So I'm working on my mom's 03 F350 7.3. the lights are acting pretty funny. She has no:

• brake lights (no brake light over the bed either)
• rear turn signals
• rear hazards

The lights that are working:

• headlights
• front turn signals
• front hazards
• front and rear running lights
• reverse lights

I've done the obvious things like checking fuses, relays and bulbs. I've also checked the connections on the wiring harness at the rear of the truck, under the bed. What should my next step be? It throws me for a loop that the rear running lights and reverse lights are working but not the turn signals or brake lights. To me that would automatically say relay or fuse, but I've checked those. If there was a short in the wiring I would assume that none of the lights in the rear would work.

Of course, I drive an old VW beetle that's 40 years old, so my mechanical knowledge isn't necessarily applicable to modern vehicles.

Thanks for any help

 

I assume she has parking and marker lamps on the bed working? If so, begin by checking the Multi-Function Switch.

 

There are no marker lamps on the bed. The only lights physically attached to the bed are the tail lights. If you're talking about the light over the bed attached to the cab, the brake light doesn't work, but the parking light does.

 

one thing that has me stumped is the bed brake light. it does not go through the multi function. it taps off right after the brake switch and goes straight to the light over the cab.


Suggest you check fuse 34 again, with a meter if you have one.

 

Check out the trailer plug and harness I have see it cause several problems that stumped me for hours

 

I actually just asked her about it, and apparently the bed brake light has been burnt out. So I'm going to get that replaced tomorrow and see what happens then. I was just assuming that it wasn't working for the same reason as the other brake lights, but it may be working after all.

I checked 34 and 18 visually, and they looked ok, but I'm picking up a pack of fuses tomorrow to switch them just to rule out another possibility.

 

like PFW said signal comes from Multi Function switch(Turn signal switch in the column). Rear brake, turn, and hazard use the same the wire for all three functions but left and right are different wires, left is LG/OR and right is OG/LB. There is a connector under the brake master cylinder that is a break out leading to the back of the truck.