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Discussion Starter #1
Every time i get into my car, on the first press of the brakes, I get the brake light failure message. All the lights look to be working fine.

Things I've done:
Replaced all the brake bulbs
replaced one of the tail light sockets that looked a bit rough

What else should I try/look at?
 

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Replace your car to newer one. Older 9-5 reminds to press brake to check brake light condition (and activate cruise to standby).
 

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Remember, brake lights have two filaments. If both rear brake lights illuminate-check the tail lights at night. If one bulb is brighter than the other the bulb it's in backwards. It shouldnt be possible, but it happened to mine. I had another tail light "receptacle" in my trunk/boot that I swapped it out and the error went away. It was just made incorrectly which allowed the bulb to be in backwards. One filament is brighter so I would only get the brake light message if I stepped on the brakes the first time.
 

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I chased a rear light failure (not brake light failure) message for almost two years changing out stuff and never found it. I just lived with it, the lights were working.
 

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I believe I recall my mechanic saying that there is often a wiring fault around the hinges of the trunk.
 

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I had the same issue on a 1999 9-5, I finally fixed it by removing the third/high brake light and wiggled all the little bulb connections and it fixed the problem.

All the bulbs were working but somehow there was enough corrosion (barely visible) to send the bulb failure message.
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Every time i get into my car, on the first press of the brakes, I get the brake light failure message. All the lights look to be working fine.

Things I've done:
Replaced all the brake bulbs
replaced one of the tail light sockets that looked a bit rough

What else should I try/look at?
What bulbs did you use?

When you say the bulbs look to be working, that's with the brake lights on?

I don't know your exact model and year, but it most likely specifies a 21W5 bulb for the brake/tail light. Get a good quality pair of bulbs. Canadian Tire sells Sylvania bulbs, but you have to hunt through to find the euro-equivalent bulb, Sylvania 7528 should work. Look for the wattage ratings on the package, made in Europe somewhere, and two elongated contacts on the base.
 

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Discussion Starter #8
This is a 2006 saab 9-5 sedan

I replaced rear bulbs with a set of phillips p21/5W
Both filaments work. When the brake are not pressed there is a dim light, when they are pressed the light is bright.
The pins on the bulb are offset, I don't think i put them in backwards, but i'll check.
I had someone press the brakes for me. Both tail lights work and the five top mounted bulbs work

I'll take a look at the top mounted brake light socket and report back
 

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Discussion Starter #9
I checked the top mounted taillight connector and it all looks good.

At some point one of the rear light harnesses had been repaired, and when you go back far enough in the harness I can see that it has been spliced together using electrical caps. What are the odds that this is the cause of my issue?
 

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This is a 2006 saab 9-5 sedan

I replaced rear bulbs with a set of phillips p21/5W
Both filaments work. When the brake are not pressed there is a dim light, when they are pressed the light is bright.
The pins on the bulb are offset, I don't think i put them in backwards, but i'll check.
I had someone press the brakes for me. Both tail lights work and the five top mounted bulbs work

I'll take a look at the top mounted brake light socket and report back
It's not so much the pins are offset (they have to be). The contact buttons on the bottom of the bulb need to be elongated, at least on a 2003 9-5. Bottom contacts that are dots (there will be two of them) don't work well in the sockets in my 2003 wagon. They may have used a different socket in later cars, I don't know.

Although checking that dubious connection is a good idea. Also check grounding.
 

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Discussion Starter #12
the 2006 and onward 9-5's have a different light socket.

I finally got around to properly repairing the harness. Turns out this was not the issue. I still get the brake light failure message. Ground looks good too, any ideas on what I should check next?

273744
 

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Which actual P21/5w are they? There are both 1157 and 7528 bulbs. Both are also known as 21/5w BUT, they are not the same bulb.
Everywhere I looked shows the 7528 as being the correct bulb for the tail light/brake light which echoes what EDT suggested.
 

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Discussion Starter #14
Which actual P21/5w are they? There are both 1157 and 7528 bulbs. Both are also known as 21/5w BUT, they are not the same bulb.
Everywhere I looked shows the 7528 as being the correct bulb for the tail light/brake light which echoes what EDT suggested.
I'm not sure. I just asked the parts shop for some p21/5w bulbs as thats what the manual says, I assumed that they were all the same. Got a pack of phillips bulbs. I cant remember if they had any other code. They looked the same as what was already in there, and work fine when the brakes are pressed. I will pull out a bulb tomorrow to see if I can get any more information off it.
 

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Discussion Starter #15
It's not so much the pins are offset (they have to be). The contact buttons on the bottom of the bulb need to be elongated, at least on a 2003 9-5. Bottom contacts that are dots (there will be two of them) don't work well in the sockets in my 2003 wagon. They may have used a different socket in later cars, I don't know.

Although checking that dubious connection is a good idea. Also check grounding.
I reread your reply, I must have misunderstood it at first. I thought you were referring to the two locating pins on the side. I looked at the bulbs I have in the car, and they have the dot style contacts. I'll see if I can pick up some cheap bulbs at Canadian tire and will report back.
 
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