I didn't see your original comment, no I don't have a test light and that's not what my ground looks like. I can take a picture tomorrow of the harness & ground if that helps.

 

You may want to check or run a wire from the NEG post of the battery to the frame.
The frame is insulated from the body by rubber so if you do not have a wire (10GA) running to the frame from the battery neg post it may only be a grounded intermittently.

 

Ok sounds like a plan. When I get home I'll run a wire to the frame of the truck and see how that goes. What if I literally ran a wire around the truck from the battery to the harness? Would this give the same effect while I'm trying to diagnose the problem?

 

Welp, I've done what subford recommended to no avail. All lights still work aside from the brake lights. I've checked just about everything in the system that could be a problem and I'm honestly at a loss. The only possible (not really) thing it could be are the bulbs, which still both contain two undamaged filaments. I don't know why this would be the problem, but it's the only thing that I can think of at this point.

 

AGAIN. do you own a test light?

 

Post #16..........

 

That doesn't matter.Eventually,every item will fail on a vehicle and at some point it was working fine the day prior.Remove that ground wire,take and clean up the frame where the screw goes into,clean up the ring terminal,then apply some grease to the area and screw the screw and wire back in.Chances are high the issue will be resolved.

Be sure to remove the bulbs,spray the sockets with electrical cleaner (WD-40 does work pretty good too,I've used it when I ran out of e-cleaner) apply some bulb/dialectic grease and put the bulbs back in.

 

Get yourself a test light and multi meter

 

Thanks for the help everyone, in response to @FORDF250HDXLTordf250hdxlt, I had already touched up the ground at the back of the truck and ensured the connector was nice and clean. The problem DID turn out to be that "ground" though. I tested it on a multi meter (I do have one Diesel_Brad btw) and there was resistance even on the bare metal I had ground down. So I said ok, that's probably my problem. There was a ground wire that runs with the harness to the front of the truck aside from this wire so I decided to give it a try without that cable connected. It works now. What I don't understand is how this problem all of a sudden sprung up. and if my frame really isn't grounded anymore, will that short any other components? I only bought this truck about 3 weeks ago and I've only owned cars so I'm pretty new to this.

 

The easiest way to make sure every thing is grounded is to ground it yourself. ground cab to frame and bed to frame then ground from battery to frame. I chased grounding problems all over a Chevy I had. I finally bonded everything together and the issues went away. Corrosion takes many forms,often caused by dissimilar metals being in contact with each other.

 

 

https://www.fordf150.net/forums/viewtopic.php?t=32879 Lots of possible issues. Check this thread out for some good ideas for you. Sandy