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Old 04-21-2018, 01:15 AM   #3
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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.

Originally Posted by autostaretx View Post
Step One: circuit diagrams are section 8W of the full 2006 service manual:

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
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