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Ask Lou P. master tech Your Own Question
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4487
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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My Trailer lights aren't working, The lights on my trailer

Customer Question

My Trailer lights aren't working
JA: Just to clarify, what are the exact lights you're talking about?
Customer: The lights on my trailer when connected to my mercedes
JA: What is the model/year of your Mercedes?
Customer: 2010 ML 350 bluetec
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I just had it at the dealer but im running out of time and I have to travel to Nebraska so im in a time crunch. They keep saying its coded for trailer lights. I get power to the fuse. (70) power to my hitch 7 pin along with a good ground. and power to my electronic brake controller (fuse 71) (and the controller itself lights up) But none of the other pins work. (Brake lights, backup lights, turn signals, running lights) at the 7 pin socker socket*
JA: OK. To minimize me, please click the down arrow at the top right corner of this box.
Customer: ok
JA: Anything else you think the mechanic should know?
Customer: That I have had the rear sam "coded" today. I have all MBZ parts. I have relay U installed. If he can help me fix it is there a way I can check if the rear sam was coded correctly? Im open to trying anything and im handy with a volt meter or test light
Submitted: 10 months ago.
Category: Mercedes
Customer: replied 10 months ago.
My vin Is 4JGBB2FB7AA555042 if you can check to see if its really coded or not
Expert:  Lou P. master tech replied 10 months ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 10 months ago.

first question i have for you as well is , is the trailer a led lighted trailer or normal incandescent bulb trailer?

Expert:  Lou P. master tech replied 10 months ago.

here are your vehicle codes


218Reversing camera

21R5-spoke design 48.3 cm (19") light-alloy wheel

232Garage door opener (frequency range 284-390 MHz)

249Interior mirror and driver's exterior mirror autom

275Memory package electrically adjustable driver's se

280Leather-covered steering wheel/shift lever

293Sidebags in rear

299PRE-SAFE® system

301Ashtray package

345Windscreen wiper with rain sensor


414Electric sunroof, glass version


438NECK-PRO luxury head restraint

441Steering column

461Instrument cluster with display in miles and Engli

474Diesel particulate filter

475Tyre pressure monitoring system

494US version

500Electrically folding exterior mirrors

512COMAND APS with DVD-changer

517HD - Radio

518Media Interface including consumer cable set

524Transport protection

551Anti-theft alarm system

580Air conditioning system

636Omission of warning triangle

666Freight packaging without tie-down hooks

673High-capacity battery


720Roof rails in black

723Luggage cover

731Wood finish, burr walnut trim

763Key with Radio remote control with panic switch

800Technical modifications

840Heat-insulating dark-tinted glass

846Aluminium-look running boards with rubber studs

866Pre-installation for Rear Seat Entertainment Syste

873Heated front seats

890EASY-PACK tailgate

904Basic package

989Identification label under windshield

A05Desigation not recorded

A21Desigation not recorded

A22Desigation not recorded

A49Desigation not recorded

A52Desigation not recorded

J1ADesigation not recorded

J52Desigation not recorded


K15Desigation not recorded


P94Appearance Package

R02All season tyres

R66Run-flat tyres

U10Front passenger seat with weight sensor

U12Velour floor mats

U41Fuel/water separator and lubrication package

U42Diesel Emission control BLUETEC (SCR)


U80115 V socket

V59Desigation not recorded

Expert:  Lou P. master tech replied 10 months ago.

SO U533 is for the trailer hitch and i dont see it in your option list.

did you install the hitch or ???

also the pins will NOT have power, the rear sam cuts power out to the trailer socket if it does not sense the correct amount of resistance, that is why i asked if it was led, if the trailer is led then the lights will NOT illuminate without a special adapter. hope this helps. let me know if you need more info or help, Please take a second and click the stars at the top of the screen to rate me so i may receive my credit , 5 stars is ideal , please request me in the future.
Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information if needed, Lou P.

Expert:  Lou P. master tech replied 10 months ago.

Hello, did you get the trailer issue squared away, i sent you a bunch of info and have not heard back from you or have been rated yet, did you have any follow up questions?

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