Wiring a truck cap 3rd brake light and dome light
#11
Senior Member
For those examples you could tap into the 12v at the trailer hitch with no issues. If you were running something that pulls more than 10 amps then I would run a different wire to the outlets. If you are running up front to the fuse box I would use a 16 gauge power wire just to be safe. The lower the number of wire the thicker the wire is and the more current you can safely pull through it.
As far as the 3rd brake light goes, these trucks flash the same bulb as the brake light for their turn signal. That is the same as the trailer wiring. If you tapped into just one you would get a flashing 3rd brake light when that signal was active and possibly feed voltage into all lights and computer when the brake was applied with the turn signal on. There is a dedicated circuit for the brake light that is independent of the turn signals and that should be used. I just looked at my 13 XLT and it is very easy to find the blue/orange stripe wire to tap into. Get some wire loom and tie the new wire inside the loom to the existing harness running down the frame.
Also I always use wire loom when running anything. It looks neater and gives an extra layer of protection against shorts.
As far as the 3rd brake light goes, these trucks flash the same bulb as the brake light for their turn signal. That is the same as the trailer wiring. If you tapped into just one you would get a flashing 3rd brake light when that signal was active and possibly feed voltage into all lights and computer when the brake was applied with the turn signal on. There is a dedicated circuit for the brake light that is independent of the turn signals and that should be used. I just looked at my 13 XLT and it is very easy to find the blue/orange stripe wire to tap into. Get some wire loom and tie the new wire inside the loom to the existing harness running down the frame.
Also I always use wire loom when running anything. It looks neater and gives an extra layer of protection against shorts.
for the 3rd brake light look for the blue/orange stripe wire and connect directly to that. No fues required? Run what size wire from this to the third brake light inside the wire loom?
For the 12V power plugs get 16 gauge wire (with a fuse?) and tap into the hot line of the 7 pin connector? What size wire should I use for this if it's under 10A? Then if I need more than 10A then go directly to the fuse panel with some 16 gauge wire and tap into any spare fuse with a spare fuse rated for higher than 10A?
#12
Da Dog Whisperer
In the spirit of being super clear I will do the following, please confirm.
for the 3rd brake light look for the blue/orange stripe wire and connect directly to that. No fues required? Run what size wire from this to the third brake light inside the wire loom?
For the 12V power plugs get 16 gauge wire (with a fuse?) and tap into the hot line of the 7 pin connector? What size wire should I use for this if it's under 10A? Then if I need more than 10A then go directly to the fuse panel with some 16 gauge wire and tap into any spare fuse with a spare fuse rated for higher than 10A?
for the 3rd brake light look for the blue/orange stripe wire and connect directly to that. No fues required? Run what size wire from this to the third brake light inside the wire loom?
For the 12V power plugs get 16 gauge wire (with a fuse?) and tap into the hot line of the 7 pin connector? What size wire should I use for this if it's under 10A? Then if I need more than 10A then go directly to the fuse panel with some 16 gauge wire and tap into any spare fuse with a spare fuse rated for higher than 10A?
As far as the power plugs go take a look at the wire there and match that also. Probably a 16 ga but that is a guess. Going with the same size is good, bigger can't hurt but definitely not smaller.
If you are connecting an accessory and running a separate power line from the battery you should have a fuse inline as close to the battery as possible. That is protecting from the fuse back in the event of a short. Since you are going to be connecting to the factory wiring that should all be fused.
Just to be safe I would check with Ford or a local shop that does the cap installs to make sure that is the correct wire to use. I am going off jmmec's post for what wire to use. I have no reason to doubt his information but things may change from year to year.
#13
Senior Member
What are you going to run with the power outlets? That will determine how heavy of a wire and where you get your power from. If you aren't pulling a lot of power from the outlets you should also have a line running to constant power in there. Here is a diagram of that plug. You should be able to tap into the trailer wiring for the dome light in the cap, you can use the tail light wire (#4 vehicle end) if you don't mind the running lights on to have the dome light work or the constant 12v (#3 vehicle end).
Also check this page I found. It is for the 2011 but it also has a link to where the green/black wire is for the older model to tap into. Sadly there is not an easier way other than run a wire to the front of your truck. You could make a small circuit with a couple diodes and relay that tap into your brake lights at the rear or buy a module that does the same thing. It is a lot easier and cheaper to run a wire to the front. I would also make your connections with a butt connector and black tape to keep water out, personal opinion there.
https://www.f150forum.com/f38/2011-c...e-light-83548/
#14
Senior Member
There IS a factory 3rd brake light tap. It's on the driver's side under the hood in the loom that runs across the inner fender in front of the brake booster. Simply tap into that for the 3rd brake light.
As for a 12vdc source, I always install a simple fuse panel and draw power from the battery using an 8 gauge line. I can power up to 6 accessories. I mounted mine on the passenger's side firewall. This is where I ran the lead for the truck cap power for the overhead light. Much cleaner than the install the knuckleheads at the camper store did.
here's a limited detail photo:
As for a 12vdc source, I always install a simple fuse panel and draw power from the battery using an 8 gauge line. I can power up to 6 accessories. I mounted mine on the passenger's side firewall. This is where I ran the lead for the truck cap power for the overhead light. Much cleaner than the install the knuckleheads at the camper store did.
here's a limited detail photo:
#15
Junior Member
On my 08 screw there is a green wire capped and folded back on the frame at the drivers door. This is for the third brake light
. Wired mine today and works fine.
. Wired mine today and works fine.
#16
Junior Member
2015 Cap wiring
Looking for some help finding the wire for the third brake light and dome light for the cap.
I've read the previous posts about the dead end wires in the loom on the driver's side, but I can't seem to find them on my 2015.
Anyone with a 2015 that can help?
Thanks,
-Erik
I've read the previous posts about the dead end wires in the loom on the driver's side, but I can't seem to find them on my 2015.
Anyone with a 2015 that can help?
Thanks,
-Erik
#17
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Join Date: Apr 2017
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I'm also stuck. Thought i would tap into the trailer hitch wiring but that causes 3rd light to flash with directional. I have an 05 f150. Also cant find that spare wire i keep reading about.
#18
I see a number of references to the blue/orange wire that is used to connect to the third brake light (CHMSL) on my Leer cap. I found the wire and checked with a multi meter and the wire was getting power when brake pedal depressed. So far so good. But then the wire stopped displaying power. I may have shorted out the line. Does anyone know where the power comes from and if it controlled by a fuse? Thanks.
#19
I know it's been a while, but on my 05 Lariat Screw, the 3rd brake light wire was a capped off green wire right behind the trailer tow 7 pin harness.
#20
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I'm not getting any power at the green wire when I press on the brakes. Is there a fuse for this wire? The brakes come on but no power at the green wire. Please help me.