2010 basic. Own the car for 3 months and all of sudden the Break lights will not turn off. I have to pull the fuse for them to turn off. I've traced all the wires I can find to see if anything is exposed, I replaced the brake light switch. I saw a YT video on water leaking by the air filter so I removed and cleaned/vacuumed that department out and it seemed to fix it for a few weeks. But now they are back to staying on and cleaning the air filter area didn't work. It started after an automatic car wash once, but have had a car wash since and it didn't act up. I'm Lost! Anyone else had this problem and knows of a fix!? open to all suggestions!

 

Sounds Smart Junction Bow Related, has the right passenger floor been wet after a rain or car wash?

 

No, I haven't seen water on the passenger floor. where is the Smart junction box located? There was a box on the passenger side on the side of the trunk, all looked good with it. Today I did pull out the drain tube plugs in the air filter cabin and they were clogged with gunk. While doing this the light started to flicker and turn off and on. I don't understand how this area is causing the problem. How is water or something getting to the brake light wires or whatever?

 

Smart Junction box is the back side of the fuse box inside the right kick panel, when the cowl drain plugs up water sometimes gets into it from up above. Smart junction box has all the memory in it with a few computer chips and just about everything runs though it.

 

There ya go. Yep, water on the SJB, the flickering pretty much proves it. And the SJB is a control box that interprets things you want from various inputs (window switch, turn signal switch, brake light switch on pedal) as a low power signal system, then sends the high power to the devices in question and/or runs them (tells the window to move, makes the turn signals blink, turns on brake lights.) If this thing gets wet, it gets confused due to shorts and does what it wants.

Thankfully the airbags have nothing to do with the thing except maybe having a 'howdy, I'm working' signal for the SRS light in the dash, otherwise that'd be fun.

Anyway, the cabin air box leaks right into the kick panel when it's full. It's just the happenstance way of how it's designed in the car. They didn't expect the drains to get plugged when designing it, as... y'know... drains. They designed those so it should work correctly and all.

Silly humans.

Result: When the thing gets full of water at some point it's overflowing out and the path happens to lead to the SJB and tada, shorted box. Yay.

The updates later down the road were not to fix that overflowing water thing. It was to put in a shield over the SJB to prevent the water from intruding and instead go around and into the rest of the car where it's less of an electrical problem and more of a 'my carpet's wet' problem.

There is also a cowl/windshield/A-pillar issue on some of them that'll produce a similar result, but it sure sounds like yours is the cabin air box.

And unfortunately... it may be that the SJB has to be replaced as this one is already toast and is going to get worse, likely. Perhaps not. I would hope not. But I do want you to know that's a possible.

Good luck, and welcome to the forums!

 

Interesting coincidence -- my 2010 brake lights have been staying on sometimes lately also. This seems to happen when I am parked with the parking brake on; but I'm not sure how that would relate, probably a coincidence.

if I press/wiggle the brake pedal, I can get them to go off.

I have checked my cowl drains recently and they were clear; and I usually park my car in the garage; but I did park it outside during some heavy rain recently, so I guess I better have a closer look.

 

Thank you for the great explanation of why this possibly is happening!

So if I take a look at the SJB what would be an indicator that's the problem? just that it might be wet? make sure all the plugs are tight? pull it all out and dry it? Is there a way to test it?

The brake lights were staying on yesterday after cleaning out the drain pipes, so I starting wiggling all the wires around in that kick panel like an angry mad man! yup, that worked, the lights went out. I got my son to come to watch the light and slowly wiggled all the connections and wires one by one again to see If i could pinpoint it... but nothing they stayed off. Don't get me wrong I'm happy it's back to normal... But I'd really like to find where the problem really is so I can fix or replace it.

 

@Bret Let me know if you find the issue... could possibly be the same problem. But sounds like your might be the Brake light switch is sticking if you can wiggle the brake pedal and it works.

 

I agree on the brake switch for that one, Bret. Sounds most likely.

As far as how to tell what's going on with the SJB, you'd have to take off the passenger kick panel and get it out of there to inspect the entire box. May mean full extraction, which one should do with the battery positive disconnected and waiting about 20 minutes, then get it out.

You'll be looking for wetness as an obvious situation in that cavity, but even if it's not wet 'now', the evidence of corrosion (green crusties, white ashiness, that kind of thing) is what you're really looking for. If you see nastiness in/on the SJB, you might can clean it up, but that's iffy. The reality is that if the SJB starts showing signs, it's possibly not long for the world and needs to be looked at with that sidelong askance look as you continue to trust it knowing that the thing got messed up before...

...but then, that's me the paranoid one.


Anyway that's the deal. The fix? Get another SJB and have it programmed unless you get an *exact model* replacement. Aka, all the same options (or at least the ones that matter? IDK, it's weird.) Things like it's a coupe, a V8, it's got a Shaker, its a manual... It's a 2010, not an '08... I'm not sure the combo exactly, but if one or two items is not exact in the box, then the box will have to be programmed to the car. At least, that's what's in my head. Seem to recall a thread of yore what this was discussed when someone got one but it wasn't quite right and wound up getting it programmed... And you're probably looking at a used one, as new ones? Not sure they even exist... hang on... Nope, don't see it at Lakeland Ford Parts, so at least Ford doesn't have it...

Alternatively... if you're adventurous and stuff... you can get the wiring diagram and rebuild it. I'm sure that's not easy, but it's also possible to do. Heck, you could even move it elsewhere, like the trunk, if you really wanted. It's just a box.

...I'm probably just buying one and fixing the leak before that.

---

Edit: I forgot to mention inspecting of the connectors to the SJB and wiring thereto as well. Might be that. May be both. Probably not just wiring/connector only, but could be. Sorry for the omission, and thankya!

 

Thank you once again. Very informative and helpful. You are what make forms so great! I'll see what I find out when I dig into it.

 

Dangit.

In reviewing the above (because I do that), I forgot to mention this: ALSO inspect the connector wiring. Same problem of corrosion there. And may be it alone, the SJB may actually be fine if it's the connectors/wiring to it.

I'll edit, just a small blurb. But wanted to stick that in there.

Just tryin' to help, we're all in this thing together and such!

 

thankfully my issue seems to be simple stuck switch, seems to be better now after some wiggling