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Brake Light Problem- VERY Detailed

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Old 03-19-2011, 01:49 AM
wallace7777 wallace7777 is offline
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Exclamation Brake Light Problem- VERY Detailed

This is my post on another Dodge forum that seems to not be of any help beyond jokes or instructions how to change a lightbulb... not very technical, you guys seem to be much more technically savy so I registered to see if I can find a new home?

Have been having a problem with brake lights staying on with the key in run but work properly with the ignition off. The third light works correctly all the time no matter the position of the ignition key.

Post is as follows...


Ok, got in my truck to leave work and brakes were on again and my cruise doesn't work. Went back to the truck later this evening and the brakes were back off and the cruise is working. I need someone with a good wiring diagram of the truck to chase this down for me.

When it is messing up the facts are as follows...

Brakes work, go off and on by brake switch, with key turned off. (this would rule out the idea that it is the brake switch I am thinking)

Turn the ignition to run and brake lights light up and only the third light (over the cab) actuate on and off by the brake switch, the main brakes just stay lit. Drive down the road and the cruise doesn't work.

Turn the ignition off and sometimes the brake lights don't automaticaly come on and work as they are supposed to and the cruise works perfectly.

This is intermittent, once you have the failure and the brakes lights stay lit, they don't ever start working right again until you turn the truck off and back on. (sometimes takes a day or so of starting and turning off the truck before it goes back to normal)

When you do restart the truck and the brakes and cruise are working properly, they don't fail or go back to being messed up until after the key is turned off and back on. (sometimes doesn't go back to acting up for a day or so)

This is why I am thinking it isn't an intermittent short or the like because the key has to be cycled for the problem to start again or the problem to go away.


I have disconnected the brake switch when the fault is occuring and the brake lights stay lit. (haven't disconnected when the lights are working properly to see what happens)

I am thinking I have a problem with the FCU(Forward Control Unit), the internal relay for the brake circuit is getting stuck closed causing the issue and also triggering the cruise not to engage(it does light up in the cluster it just will not set). I am just having a hard time confirming this due to my very limited wiring diagram and not knowing how the brake lights and cruise are linked... electrical signal or mechnically linked directly at the brake switch or if they are two different mechanical circuits.

I just want to confirm my thoughts before I buy the $250.00(FCU) part that I can't return only to find out it is the IPM (integrate Power Module or "Fuse Box") which has been the cause of a lot of grief for others and costs $408.00.

Can anyone tell me if it can be the FCU(Forward Control Unit) - why or why not? Or if it can be the IPM (Integrated Power Module "Fuse Box") - why or why not?

Eveyone's help would be greatly appreciated!!!

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Old 03-19-2011, 07:49 AM
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olyelr olyelr is offline
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Maybe you need to flush your blinker fluid with some of that new synthetic stuff?






















































Ok, JK. Welcome to DF!!!

There are a few of good electrical gurus on here that should be able to steer you in the right direction. Me, well I'm not one of them.
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Old 03-19-2011, 12:36 PM
T-Muns T-Muns is offline
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This is interesting. I think the "FCU" you are talking about actually the FCM (Front Control Module). I have a very similar problem, but I just did an engine swap from 4.7 to 5.7 and haven't completed the cruise circuit yet, so I clearly have a wiring issue. This leads me to believe you also have a wiring issue, especially if it is intermittent. However, I guess it could be something with the FCM or IPM as well.

The 3rd brake light is wired straight to the switch so I agree your switch is prob fine. It might help if you can tell us what year and model truck you have.

Sorry if this isn't much help, but you might just want to hit up some junkyards and try swapping out the FCM and IPM?
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Old 03-19-2011, 12:59 PM
wallace7777 wallace7777 is offline
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Ok, here is a little more about it. Right now the brake lights are working properly so I disconnected the brake switch and with the truck on the brakes come on. I reconnected the switch and the fo back off. I found a schematic for my Dodge 2003, by the way, and there seems to be a separate 12v ignition wire going to a third circuit in the brake switch and I think operates the brakes while the truck is on. There is another for the third light and another when the ignition is off. The reason I say this is I also found a 12v circuit going to the cruise from the brake switch... Therefore, I think the switch fails and a relay connects making the lights come on. Never realized when it fails it makes the brake lights come on. I was only able to check it when the lights were messed up before. This is all pointing me back to the brake switch now... Will let you know.
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Old 03-19-2011, 01:03 PM
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"you guys seem to be much more technically savy so I registered to see if I can find a new home?"

kind of an oxy moron...I don't come here for the technical stuff... with that said, if you think it's the fusebox (where the Fcm is attached to), get one from a salvage yard (I got one for $75), this solved a huge problem I had (not related to yours), but I had my guages intermittently go out, my headlights would go on and off for no reason etc, and worse, I would be driving and the truck would just shut off... last place for me to think was the fusebox until someone told me he had the same issue years before and finally solved it by replacing fusebox with fcm (info from the 'other' place)
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Old 03-19-2011, 02:07 PM
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hey wallace welcome to the forum....almost a month ago i had the same prob. what you need to do is where the brake pedal is, follow the metal bar all the way up into undearneath the dash, your gonna see a little box with a kinda puch switch sticking out, thats what controls your brake lights to come on and off...then head to oriellys and pick you up a new one. i paid $11 for a new one. if you want, you can do everything right in the auto parts store parking lot, only takes a total of 10-15 min. also best part, is you dont need any tools to fix this...BTW your see a small harness connected to it, unlock the red clip then pull the plug, then turn the module a 1/4 and then it comes right out.


here a link to see what the switch is goin to look like

http://www.carparts.com/details/Dodg...pc506602337554
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Old 03-19-2011, 02:22 PM
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didn't i tell you on the other forum to check the brake switch lol
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Old 03-19-2011, 03:43 PM
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I had a similar problem and it was the TIPM. $1,100 from the dealer. check my created threads to read a little about it
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Old 03-19-2011, 06:06 PM
wallace7777 wallace7777 is offline
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Marx, you said to check the adjustment which there is none, however, you did mention the switch may be bad and for that I appreciate you. The other forum I had three posts in a row from another guy telling me to check the washer fluid, downloads for the daytime running lights etc., I was frustrated with that guy by the time you posted.


Like I said previously, there are three circuits in that switch mechanism and from my and everyone elses experience, when a brake switch fails they tend to not light... not stay lit all the time as mine where doing. I pressed on the switch and plungered it by hand when it was messing up and saw no responce but I guess it gets hung internaly and won't release or something. The 12v power coming from the ignition was getting me too. It had me thinking I may spend a bunch of money replacing everything and because it is intermittent, I would have no clue what fixed it.

Also, the erratic lights, dash console light problem and the like is considered a PCM problem but is not what fixed mine and was not the same symptoms I was having... it was a $11.00 switch from Autozone. If anyone ever needs pages from the 2003 service manual just email me, it really helped me trace all of this down and backup the theory it was the brake switch.

Thanks again everyone, special thanks to Marx!

Last edited by wallace7777; 03-19-2011 at 06:08 PM..
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Old 03-19-2011, 06:27 PM
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Now, off to find me a Toyota 4x4 to take to my deer lease... this Dodge is falling apart.

I have replaced the rear-end guts with an Eaton Detroit TruTrac system because I got bit by the c-clip problem and destroyed my pionion and bearings.

A/C condensor fan caught on fire and had to be replaced.

New wheel bearings at 125,000.

My dash all of a sudden is falling apart(cracked all over the place in the last 3 months)

Spent $5000.00 on a new engine at 118,000 miles because the 2003 Hemi had bad valve springs in it and are suseptable to cracking and dropping a valve. There is even a service bulletin on it, if you have brown markings on your 2003 Hemi Valve springs, get them replaced. Dodge used brittle springs in the 03 and never did a recall... they just figured they would take their chance and only repalce these under warranty if they had to. I am sure the Service Bulleting is mentioned some place on this forum.

Would be nice to be able to recoupe at least some of my money for the new engine but I guess I am S.O.L. on that since my warranty was out. I loved my truck and its performance up until a few thousand miles ago. I just have about $5000.00 in a stereo system and $5000.00 in a new motor or I would trade it away today. You will never catch me buying another Dodge again... sorry guys.
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Old 03-19-2011, 06:27 PM
 
 
 
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