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Hello one and all,
I have a problem! I have been searching the forum for about a week for an answer to the question of where to splice a wire for the 3rd brake light on a cap. All the wiring discussions have left me dizzy.
Perhaps more info would be beneficial for you. In February, I bought a ‘16 F150 XLT Supercrew FX4 with a 3.5 EB. Last week I located a used ARE cap for a 5.5’ bed. A little pricey, but still less than 1/2 the price of a new one. So began my search for wiring (not my strong suit) knowledge. I’ve read everything I can find about the subject, and am more confused today than I was at day 1. One question that keeps coming to my mind is: This rig came from the factory with not 1, but 2 trailer connectors for lights. Why can’t I simply splice into either of those for power to the caps 3rd brake light?
Does any of this make sense to any of you? If it makes no sense, can you tell me why?Any help would be greatly appreciated.
Have a great day,
TT
Because trailer lights are wired so that L Brake and L Turn Signal are together, and then you have R Brake and R Turn Signal tied together.
The third brake light is obviously tied to the brake light switch somewhere before it was intertwined with the turn signals.
You say there are two trailer connections, is it a round RV plug next to a 4 pin flat? Or is there an additional one inside the box? You usually see the one in the box there for gooseneck trailers....
litter-5.0
Thanks for your reply and input. My setup is a 7 pin round above a 4 pin flat, both connectors in the rear bumper. Maybe I’ll break out the he little light up probe, ground it, get the wife to help me and start poking around on wires at the bed of the truck.
Thanks again,
TT
On my 2018, all the wires ended up being in the drivers side door sill. It seemed crazy to me as well and I spent a lot of time with a meter testing wires at the back of the truck, in the end it would have been way faster to just run the wires up to the door sill like o did in the end.
Ibewebbman,
Mind if I ask how you ran the wires out of the cab? Is there a pre-existing exit point at the rear of the cab, perhaps behind the rear seat?
Thanks,
TT
There is a thread on toppers, look for a post I did with pictures. There is a purple/white wire in the drivers side kick panel, the one in the black connector. You tap that for the 3rd brake light. Under the carpet on the drivers side is grommet where you can fish the wire through. I would repost the pics, but facebook and this forum are not getting along.
acdii,
Well, it seems that the search function and I don’t really get along at all. I can’t seem to find the thread you mentioned. I’ll keep trying the search button and may get lucky at some later time.
I think I’m going to try a fuse tap at the BCM. I’ve read that is that the simplest way. I just can’t wrap my mind around Ford making it that difficult to add things they know a lot of people use. I guess the schools no longer teach the K.I.S.S. principle.
At any rate, I thank you all for your help, and hope you have a great evening.
TT
Maybe this will help. Some info I came across (here in the forum somewhere) and kept a copy for later reference. See attached notes (PDF files). I'm not sure if the 2nd PDF will upload or not, it just shows the location of the connection. Hope this will help get you going in the right direction. Of course there are many ways to wire this up, but if I were to do this, I'd use the purple/white wire to engage a relay, which provides the 12V to the topper/cap (see attached JPG file).
breakers28,
thanks a million for this info. I had seen the convo, not really paid it much attention and then couldn’t find it again.
I tried all the wires in the green loom that runs under the panel under the door sill yesterday and had no (good) luck. In my frustration I ordered some fuse taps because I knew I’d read somewhere to run the wiring from the BCM.
thanks again for your help,
TT
acdii,
Well, it seems that the search function and I don’t really get along at all. I can’t seem to find the thread you mentioned. I’ll keep trying the search button and may get lucky at some later time.
I think I’m going to try a fuse tap at the BCM. I’ve read that is that the simplest way. I just can’t wrap my mind around Ford making it that difficult to add things they know a lot of people use. I guess the schools no longer teach the K.I.S.S. principle.
At any rate, I thank you all for your help, and hope you have a great evening.
TT
Really simple, pull the threshold up, pull the weather stripping from the front, pull the side panel, and there they are. Tap the purple white on the black connection, which is on top. Run the wire under the carpet to the grommet in the floor and run that back to the bed and up the side. This is the dedicated 3rd brake light wire to use for the topper per Ford. Try not to do anything BCM related as it could cause damage.
06-18-2019, 02:10 PM
Cap 3rd brake and dome lights
