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Old 04-20-2018, 04:17 PM   #1
chrisslondon
 
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Default Brake lights remain on - Accessories run when brake pedal pressed

Hello All,

I have a 2005 Sprinter 3500 (Freightliner) that carries a Gulf Stream Vista Cruiser Mini motorhome.

This winter on January 8, 2018 I noticed the brake lights on the motorhome. I had used it December 18-20 2017 and nothing was out of the ordinary then. I couldn't figure it out then so simply removed the wires from the light bulb assembly as I couldn't figure out what fuse to pull.

I took it to the mechanic on April 9th after replacing the brake light wires so I could drive it safely. No brake lights showed then and also the brake lights did not light when the brake pedal was pressed. The mechanic found a broken wire in a maze of wires that are part of the Signal/Brake system installed to allow for North American trailers to plug in.

After using the motorhome on April 13th, I noticed the brake lights on again the next morning. When I press on the brake pedal, the heater fan begins to run and the dash lights light up. That's a bit weird. If anyone can offer help with this problem, I will be more than pleased as the Sprinter goes to the mechanic next Monday.

Thanks,
Rob
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Old 04-20-2018, 05:21 PM   #2
autostaretx
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Default Re: Brake lights remain on - Accessories run when brake pedal pressed

Step One: circuit diagrams are section 8W of the full 2006 service manual: http://www.diysprinter.co.uk/reference/2006-VA-SM.pdf

As many many threads in this forum describe, seemingly unimportant problems in the tail and license plate light units (or owner-added trailer hookups) can cause actions such as "engine continues to run after key removed". Water at the base of one of the two rear pillars can corrode even the official MB trailer tap-off unit.

The brake pedal has two switch sections: one controls the brake lights, the other informs the Engine Control Module that you're stepping on the pedal.
Has anyone taken a voltmeter to the brake lights while a helper steps on the pedal? Have they checked the continuity-to-ground (frame) from the light units?
Have they really scrutinized the tail light unit circuit boards for cracked traces, broken solder joints and loose metal bars?
Have they verified that both of the dual-filament brake light bulbs are properly oriented in their sockets?
...and that the above-the-door top lamp is happy?

Unfortunately, you're kind'a in for a tedious hunt looking for the true fault, and some bits (such as voltmeter verification) require two people (at least one only needs to contribute a foot on the pedal, not electronic expertise).

good luck hunting
--dick
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2005 T1N 118" Freightliner 2500 Passenger Wagon (2.7L, 15" tires, standard (short) roof)
http://diysprinter.co.uk/reference <-- lots of service documentation, Thanks to Jens Moller and Arnie_Oli
((as always: this post may go through a couple of post-posting edits... so maybe give it ten minutes before commenting))
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chrisslondon (04-21-2018)
Old 04-21-2018, 01:15 AM   #3
chrisslondon
 
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Default Re: Brake lights remain on - Accessories run when brake pedal pressed

Thank you Dick for this help. I'll pass it on to my mechanic who is a very good one.
Rob

Quote:
Originally Posted by autostaretx View Post
Step One: circuit diagrams are section 8W of the full 2006 service manual: http://www.diysprinter.co.uk/reference/2006-VA-SM.pdf

As many many threads in this forum describe, seemingly unimportant problems in the tail and license plate light units (or owner-added trailer hookups) can cause actions such as "engine continues to run after key removed". Water at the base of one of the two rear pillars can corrode even the official MB trailer tap-off unit.

The brake pedal has two switch sections: one controls the brake lights, the other informs the Engine Control Module that you're stepping on the pedal.
Has anyone taken a voltmeter to the brake lights while a helper steps on the pedal? Have they checked the continuity-to-ground (frame) from the light units?
Have they really scrutinized the tail light unit circuit boards for cracked traces, broken solder joints and loose metal bars?
Have they verified that both of the dual-filament brake light bulbs are properly oriented in their sockets?
...and that the above-the-door top lamp is happy?

Unfortunately, you're kind'a in for a tedious hunt looking for the true fault, and some bits (such as voltmeter verification) require two people (at least one only needs to contribute a foot on the pedal, not electronic expertise).

good luck hunting
--dick
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Old 04-21-2018, 04:57 PM   #4
autostaretx
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Default Re: Brake lights remain on - Accessories run when brake pedal pressed

If he's a Sprinter mechanic, he'll know the following, but if he's not, here it is:

The Sprinter's brake pedal switch sometimes needs to be "reset", which is done by:
(a) crawl into the pedal area (engine off, no key needed)
(b) press the brake pedal by hand as far as you can
(c) locate the switch's stalk that is released when the pedal arm moves away from it
(d) gently *pull* that stalk out as far as it wants to travel
(e) gently release the brake pedal so everything returns to their normal positions.

(that usually helps the ECM half of the switch, not the lights, but it's quick and easy and can't hurt)

--dick
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2005 T1N 118" Freightliner 2500 Passenger Wagon (2.7L, 15" tires, standard (short) roof)
http://diysprinter.co.uk/reference <-- lots of service documentation, Thanks to Jens Moller and Arnie_Oli
((as always: this post may go through a couple of post-posting edits... so maybe give it ten minutes before commenting))
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ptheland (04-22-2018)

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