DIY reverse light

[urchinray]

Hi, I am new here and I need some help with my reverse light project. I would like to add an extra reverse light to my 2014 W205 C250 that came with an LED tail light. I used a horn relay and connected it to the main power as the power source for my add-on LED. I connected to the original reverse light as the power source of the relay tricker. But when I shifted into the reverse gear, although it was working, the relay started Buzzing. It didn't happen in my Hyundai when I did the same thing, The Only difference I can tell is reverse light in my Hyundai is light blub and my Mercedes is LED. Can anyone help me to solve this problem? Please check the video from my link for more details.

 

[Uncle Benz]

The lighting control will not like anything directly connected on the reverse light output other than the correct LED. You may be able to get around it by using a canbus friendly trailer socket kit and use that to trigger your relay

 

[urchinray]

The lighting control will not like anything directly connected on the reverse light output other than the correct LED. You may be able to get around it by using a canbus friendly trailer socket kit and use that to trigger your relay

Thanks for your reply. Do you think it is a good idea if I connect my add-on reverse light to the reverse light?

 

[Uncle Benz]

Thanks for your reply. Do you think it is a good idea if I connect my add-on reverse light to the reverse light?

No, I don’t think the lighting control module will be happy to see the extra load. You could try it, but it’s at your own risk

 

[V6Matty]

May be a daft question, but why do you need an extra reverse light?

 

[urchinray]

May be a daft question, but why do you need an extra reverse light?

Because I always reverse to my long, dark driveway, I want some extra light at night.

 

[urchinray]

No, I don’t think the lighting control module will be happy to see the extra load. You could try it, but it’s at your own risk

I found something interesting today. When I set my multimeter to auto to measure the power from my reverse light, it detects it as AC and the frequency is between 700 to 900 Hz. That makes perfect sense for why my relay has a high-frequency buzzing. I may try to use a diode to fix the problem. Any comment?
AC power from me C250 reverse light

 

[Trev1964]

I normally switch on the fog lights for extra light in the dark when reversing. Also gently touching the brake pedal will throw more light.
Not sure where you could mount an extra light on a modern car and not have it look weird.
I tried brighter bulbs and they didn't help.

 

[supernoodle]

I doubt it's AC, more likely just a PWM. A scope would be best way if confirming.

If it is a PWM, one way would be to make a circuit with that has a high input impedance and a filters the signal. That avoids adding too much load to the existing circuit.
An easy option if you're not into electronics would be to buy a relay module that has a transistor driver circuit built in (search for Arduino relay module). Then make an RC filter with a resistor and capacitor (values depend on frequency of signal) and connect between reverse light and the relay module.

Or put lights on the drive.

 

[urchinray]

I normally switch on the fog lights for extra light in the dark when reversing. Also gently touching the brake pedal will throw more light.
Not sure where you could mount an extra light on a modern car and not have it look weird.
I tried brighter bulbs and they didn't help.

What do you think about this one?

 

[urchinray]

I doubt it's AC, more likely just a PWM. A scope would be best way if confirming.

If it is a PWM, one way would be to make a circuit with that has a high input impedance and a filters the signal. That avoids adding too much load to the existing circuit.
An easy option if you're not into electronics would be to buy a relay module that has a transistor driver circuit built in (search for Arduino relay module). Then make an RC filter with a resistor and capacitor (values depend on frequency of signal) and connect between reverse light and the relay module.

Or put lights on the drive.dc

I agree with you, it should be a PWM. I planned to try to use a DC-DC SSD relay to see if it is work.

 

[urchinray]

In the end, I fixed the problem. I use an AC-DC relay and it works well. It doesn't mean the power from the reverse light is AC power. I still believe it is PWM because the frequency is too fast. However, an AC-DC can fix the problem in this case. I have already ordered an SSD relay, I will try it when it arrives.

 

[JohnHansen29]

UrchinRay what is the spec of the relay you used (both mechanical and solid state)? I would like to try this also.

 

[urchinray]

UrchinRay what is the spec of the relay you used (both mechanical and solid state)? I would like to try this also.

I tried three different types of relays. The first mechanical is the only one not work in this case. It was a 12V 30A DC -> DC one. The second mechanical one is a 12V AC -> DC one, that's works well. And the one I am using is a 25A DC -> DC Solid state.

 

[JohnHansen29]

I tried three different types of relays. The first mechanical is the only one not work in this case. It was a 12V 30A DC -> DC one. The second mechanical one is a 12V AC -> DC one, that's works well. And the one I am using is a 25A DC -> DC Solid state.

Many thanks.