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SJB swap

Tiny
TYLER2842
  • MEMBER
  • 2006 FORD MUSTANG
  • 4.6L
  • V8
  • 2WD
  • MANUAL
  • 131,000 MILES
Does 07-09 SJB work on the car listed above?V So my car starting acting really crazy after owning it for about a week. Today the blinker on the left side turned on even though I didn’t turn it on and stayed on no matter what I did right after that I noticed lights on my dash and my windows wouldn’t roll up. So I immediately assumed the alternator had gone and turned the car around and drove home. When I turned off the car it wouldn’t lock with the remote and the blinker was still on and blinking even though the key was out. I grabbed the voltmeter checked the car it was at 12 I started the car it was running at 14.0 so I assumed the alternator was fine. I disconnected the battery and cleaned the terminals and the battery itself. Plugged it back in started the car it was fine. Everything worked again. A couple hours later I decided to check on it and the key-less entry wouldn’t work and I had to unlock it with the actual key I use to start it, reminder mine is the one with a key and a separate fob. This time when I turned it on the brights were on and wouldn’t turn off but the actual lights in front of the car were off. So I did some research and found out about the smart junction box and I’m thinking this might be the issue just curious on what you guys think and I’m planning to buy a used one but it seems the way it’s listed the 05-06 are interchangeable but they don’t work with the 07-09. Not sure if this is true or not I could use some feedback as I can’t find the correct part number. Any feedback would be appreciated I’m going to look into it much further for sure.
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Tuesday, August 18th, 2020 AT 6:26 PM

12 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,413 POSTS
Has it rained in your area just before or during this issue? The Mustangs seem to have water leakage issues at the windshield seals which lets in water that damages the SJB in them. One thing you can try is to disconnect the battery and remove the SJB, look at the connectors on it and clean them all, then apply a dab of dielectric grease and reinstall. See if it all works now. Corrosion is a common reason they fail. As to if the 07 up part will work. The sources I have say maybe but not positive. The boxes are coupe or convertible items and those are not interchangeable, you can't use the coupe part in the conv. Or the other way either. Beyond that the part numbers need to match up to be sure it will work. Then you may need a dealer to program in some of the options.
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Tuesday, August 18th, 2020 AT 9:02 PM
Tiny
TYLER2842
  • MEMBER
  • 7 POSTS
Yes, it rained heavy the day before it started acting up. So I’m assuming it probably is the SJB. Then based on what you said I’ll give the dielectric a go and see if it helps thank you. Can’t seem to find a used 05-06 SJB only new so I’m hoping the 07-09 one will work otherwise I have to buy a brand new one.
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Wednesday, August 19th, 2020 AT 7:05 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,413 POSTS
I have had the remove, clean and reinstall work as long as you get it fully dried out. There is a TSB out there on the leak, sometimes it works, sometimes it doesn't. I know of a few folks who did the re-seal but then took the SJB out, cleaned it and then sealed it into plastic wrap to keep water out. Search Mustang Water Leak for a bunch of info and fixes. I would really try those first because water leaks can do a lot of damage, not just with the electronics.
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Wednesday, August 19th, 2020 AT 10:52 AM
Tiny
TYLER2842
  • MEMBER
  • 7 POSTS
I was thinking of using like a Ziploc bag for steak cause it should be the right size I think. I will try covering it with plastic when I reinstall that should hopefully keep the water out then. The new SJB should be here by Monday I’ll let you know how it goes. Also side note I took the car out yesterday and everything was acting fine again maybe because it had dried out but I will for sure take it out examine and clean or dry out what I need to dry out. Will keep you in the loop.
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Thursday, August 20th, 2020 AT 6:09 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,413 POSTS
If you can keep it dry most of them work fine for years. I like to take them apart all the way and clean out anything, then spray the boards with clear paint and put them back together. That is more than many want to do though. Don't forget to hunt the leak down though. Rusted out floors and moldy carpet are no fun either. You may need to have the replacement flashed if it had options different than your car activated but it depends. Either way let us know.
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Thursday, August 20th, 2020 AT 6:52 AM
Tiny
TYLER2842
  • MEMBER
  • 7 POSTS
Will do. I think the leak is coming from a small hole in my windshield where the plastic trim meets the windshield. I also noticed a small hole in the rubber part where the passenger window meets the frame of the car. So I will plan to seal or replace. I figure replace might be better but at the same time someone might do a worse job putting a new rubber seal on than me sealing the original. I will post pics when I get home and see what you think.
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Thursday, August 20th, 2020 AT 12:26 PM
Tiny
STEVE W.
  • MECHANIC
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If you can come up with a way to make smoke or even steam you can use it to find some leaks. You use the fan blower on high inside the car with it taking in outside air or use something like a leaf blower or similar in a barrier in a door window to force air into the car. Then go around the window and panel seams with the smoke or steam and look for it to move where air is escaping from the car. Like this video:
https://www.youtube.com/watch?v=WlckHdd5WoE
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Thursday, August 20th, 2020 AT 3:26 PM
Tiny
TYLER2842
  • MEMBER
  • 7 POSTS
Very clever any idea. What type of smoke machine I need for that?
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Thursday, August 20th, 2020 AT 3:47 PM
Tiny
TYLER2842
  • MEMBER
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The third pic I definitely see signs of water leaking due to the rubber starting to crack and the discoloration.
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Thursday, August 20th, 2020 AT 3:51 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,413 POSTS
Any type of smoke or steam generation would work, even something like a tin can with smoldering leaves and a hose. The idea is to use the smoke just to see the airflow. I've seen a bunch of DIY things used, from cigars, leaves, stage smoke machines.

Just a few examples of ways to create smoke cheap:

https://www.youtube.com/watch?v=GOhl4r0GSiE
https://www.youtube.com/watch?v=2U5kFib1WxE
https://www.youtube.com/watch?v=BP2ffBSD2A0
https://www.youtube.com/watch?v=9z3DEiYHqok

The base of the windshield is a common leak area on them, it then runs down the inside of the cowl panel and into the SJB. If you use a mirror and look above it inside the car and behind the panels you will likely see the deposits left by water where it ran down.
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Thursday, August 20th, 2020 AT 4:47 PM
Tiny
TYLER2842
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This is a pic of the sjb I bought online. I don’t see signs of wetness or damage. Let me know what you Guys. Think I’ll be taking out the one in my car this weekend.
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Friday, August 21st, 2020 AT 3:28 PM
Tiny
STEVE W.
  • MECHANIC
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Looks okay. If you pull the one in the car apart you can likely clean it and have it work, I would compare them very close and be sure things match up before trying the replacement.
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Friday, August 21st, 2020 AT 4:05 PM

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