2003 ml500 no brake light, a MB technician told me that I should add a stop light switch and connect wire to a relay, he demonstrated, and it works, can you tell me which relay it is please?

There are a few possible reasons why your turn signal light is not working while your brake and tail lights are functioning properly:

1. Blown fuse: The turn signal lights are connected to a different fuse than the brake and tail lights. The fuse for the turn signals may have blown and needs to be replaced.
2. Turn signal switch: The turn signal switch, located on the steering column, could be malfunctioning and needs to be replaced.
3. Wiring issue: A wiring issue, such as a broken wire or loose connection, could be preventing power from reaching the turn signal lights.
4. Flasher relay: The flasher relay is responsible for controlling the turn signal lights. A faulty flasher relay could be preventing the turn signals from working.
5. Signal/light module: Some cars have a signal/light module that controls the turn signals, this could be faulty and need to be replaced.

Don't think so, I have never heard of a relay in a brake light circuit.
Sometimes there are two brake light switches on the brake pedal, one is for the cruise control. Are you sure you don't have another switch on the pedal? If that is the brake light switch, I don't know how the lights could stay on if the switch is removed. Does it have a button that needs depressing? If the button is held in on a brake light switch, it should stop the lights from coming on...?

if there are 2 switches on the pedal one is a cruise interrupt switch the other is the brake switch. check for current coming from the brake switch. it usually twists out and you can probe the the wires on the back side of the switch. if there is current there then start working your way out the harness. also check the master plug at the back under the bed is there current there to the tail lights? if not then there may be a break in the line from the brake switch to there

Hi, this may true if you connected the trailer brake to the connector on the factory wiring harness. There are several fuses that are needed for trailer towing. In the box by the battery, fuses 13, 25, 27, 53, and 54 are needed. You will need a relay in relay slot 19 for the trailer running lights, a relay in relay slot 20 to charge the trailer emergency battery; and, if your trailer has backup lights (6 or 7 wire connector), you will also need a relay in the relay slot 15. If you did not use the factory connector for your trailer brake controller, check to make sure you have connected the controller to an appropriate power source in the truck. Please let me know if you have questions, and thanks for using FixYa.

OK try this, push and hold brake then push on the hazard switch if brake lights come on then replace the turn signal switch.

Hi!!
Check the Brake Pedal Position Switch on top of the brake pedal, the Lt Green w/Red stripe wire should always have 12v+, when brake pedal is depressed the Lt Green wire should have 12v+ also, if no power on Lt. Green w/Red wire, check fuse # 2 20A, if no power on Lt. Green wire when pedal depressed, REPLACE Switch, If there is power on both wires when pedal is depressed, check IVD STOP LAMP RELAY on the Aux. Relay Box 1 located at the Left Front of the Engine Compartment.
Good Luck!! A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa.

My friend; Try this; 1. Check the fuses & relay boxes at cabin & engine compartment for any burn fuses / relay replace if any. 2. Check for any broken / chafing wires; repair if any. Check for any dis-connected plug & or wires; re-connect if any. You may need to replace some brake pads & or shows. You may need to bleed the whole brake system. Then do these procedures to erase & rest it; Dis- connects the negative battery's cable; While the ignition switch in the ON position ?Don?t run the engine" So, for 10 - 15 minutes only. Reconnect the negative cable. Try it, & let me know if I add any benefits to you. I hope I add some thing valuable to you. Regards; MAR; [email protected]

Well, have you checked the fuse? Maybe stick another one (of the same size) in there anyway. If that's ok, then check the stop light switch. It'll be somewhere along the brake pedal linkage/ arm under the dash or under the hood around the linkage or master cylinder. Look around. You can short across the wires temporarily to see if they light up and then you'll know if that's it.

what that means is your socket is is probably shorted to your running lights there is a constant feed of voltage to that circuit. i would take a circuit probe and trace a wire to the spot of the short. good luck.