OK, well then while it's warm out, I think we're getting closer.... If the high mount stop light is out, pop the cover and see what you've got. Maybe the guy that you sold it to replaced the bulb and pinched a wire when reinstalling it. At the very least, try to unplug it and see if it stops blowing the fuse.

(Another side-thought: Aftermarket CHMSL could stand for Aftermarket Cap High Mounted Stop Light or something similar.... could be a dead pig-tail near the back of the truck to tie into for a 3rd brake light on a cap.)

If you had a dead-short in the wiring to the 3rd brake light, it wouldn't be affected until you stepped on the brakes, at which point, that half of the BPPswitch would trip the fuse. If you could de-pin that harness to confirm it's on that circuit, it narrows it down to the flasher circuit and the HMSL circuit for sure, but I think we're there. It's something on that one particular leg of that circuit, and being that the 3rd brake light is out, that could be the culprit.

 

One of the feeds from the brake sw is an isolated feed for the trailer brake controller... BTW stop at NAPA and get a breaker to keep from doing the twist to get to the fuse panel. I got type II's for all my trailer feeds, it's great not to have to get under there when I pull someone elses trailer and pop a fuse. The type II reset after power down if the short is removed.

 

I need to ask, do you have a cap on the truck ?

The reason I ask, is I see a T-Tap on one of the wires, which is not exactly factory.

 

hey ssculy, I believe that tap goes to something in the alarm to indicate when the brake lights should go on. I tried disconnecting that tap but the problem continued.

 

Typically, if it's tied to the remote starter, it kills the engine. If you hit the brakes (in an attempt to steal it without the key in it) it'll kill the engine. It forces you to put the key in and turn the ignition switch on before you hit the brakes to shift out of park.

Any updates, Matt?

-Joe

 

ahh that makes sense, that is indeed what the alarm doe3s so that would make sense .
Unfortunately I worked on this on Friday a bit and twisted my back and was unable to work on it more... by Sunday was feeling better but didn't have time to go down to my parents and work on it... I think I need to just tear the interior all out and start looking for frayed wiring or a screw through wires or something like that... but living in an apartment, with no garage, I've got nowhere to put the interior parts!

 

That is why I was asking, to make sure it was not a CHMSL on a cap or in your case, something else that needed brake lights.
When you were under the dash, did you try Joe's suggestion of unplugging the BOO switch ? I saw where you found it, and corrected a splice, but I don't see where you actually tried what Joe suggested.

 

ok yeah when I unplug it it doesn't blow the fuse but then its not lighting the brake lights either. I replaced it just in case, but it didn't appear to be a bad part.
One thing I did notice was before I blew the fuse, the rear taillights were working fine but the 3rd brake light didn't light up, even though I know the fuse was good.

 

Check the wires going to the trailer plug. It is spliced off of the high mount brake light circuit so your blown fuse is shared with the trailer tow stop light circuit.

JMC

 

Hmm that is good to know, I didn't realize that. So just follow those wires and look for a problem eh? I checked out the connector thinking maybe some of the wires were connecting when they shouldn't and it was grounding improperly or something but the connector seemed alright.

 

JMC, correct me if I'm wrong, but I believe that trailer brake light feed from the BOO switch only runs to the adapter under the dash that feeds the brake input to a brake controller through that adapter that plugs in under the dash. I believe the trailer brake and turn signal lights are fused separately and triggered by their own relays piggy-backed on the outputs from the MFS.

If you're looking at the schematics, 095-001 shows that lead to the 'Trailer Tow (stop lamp), but page 095-002 shows the actual wires (A and B from the previous page) going to the left and right trailer signal, which is what a trailer uses for the brake lights.

-Joe

 

OK maybe you guys with the factory schematics can help with this one, I briefly looked in my CHiltons but couldn't find what I was looking for. There is an unidentified wire that I can't figure out what it is or why it is there. Let me describe it, I'll take a picture tonight if it doesn't make sense.
If I follow the trailer harness from the hitch towards the vehicle (where the spare would be) it goes to a seperate plug that is attached to the drivers side of the frame. The plug then goes to the drivers side and looks like the brake lights branch off from a seperate plug from there. There is one wire sticking out of the harness that appears to end abruptly, not sure if it is supposed to or if it just happens to. It was slightly electrical taped to the main harness, and covered in another wire cover, but it is definately not attached to anything. It is a light green color with no stripes. Any idea what this wire could be?

 

That would be that wire I mentioned that they would tap into for a cap or camper high-mount stop light.

 

oops, you are correct. It goes under the dash and ends up where the electric brake switch would plug into. It is the Center High Mount Stop Lamp that I saw that goes to the rear of the truck. It passes under the air filter box via connector #150 which is gray.

Matt,

Does your truck have an aftermarket air filter set up? If it does check under the air filter on that tray where the air box used to sit. There should be a gray connector that has a light green wire. Look for problems there too.

JMC

 

Jean Marc, it does have an aftermarket air intake kit on it and I will check out those wires/plugs you mentioned and see if anything looks damaged, unplugged, etc. there.
Joe, thanks for letting me know. It did appear to have some sort of "cap" on it but not like one I'd seen before. At least now I have an idea what it is there for and I'll know that isnt what is causing my issues .