Installed LED brake bulbs (1156) into the 2013 GL450 and saw errors about the brake lamp being out. This is caused by the bulb not pulling enough current, thus the computer thinks the bulb is out.
A resistor is added in parallel to draw more current so the error does not appear on the dash.
The LED bulbs and resistors can be purchased through Amazon or other retailers.
Link to LED bulb install video:
https://www.youtube.com/watch?v=44dhRp5H6EQ
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Bad connectors you damage your original wiring