Hi Team,

I am new here. I have very basic knowledge of electronics thanks to Google. Hope I am in the right forum with this question. If not, it would be great if you can refer me to the right section.

Context: I am setting up a reverse camera on a 2005 golf mkv.

on my first attempt I directly connected the positive end of the reverse camera to the reverse light positive but it did not work. When I used the multimeter on it, the line seemed to output a very low voltage (less than 12v).

Then I bought a single throw 12v 30A relay and configured pin 30 to camera positive but connected the camera ground to the ground coming out of pin 85. This led to relay chatter. The camera functioned with distortion and turned itself off after about five seconds when the relay powered down.

Then I isolated the 85 ground and grounded the camera somewhere else. This eliminated the chatter but the relay turned off after about five seconds again. This is the correct operation but should power down when reverse is disengaged.

Does this mean the trigger voltage is not enough to hold the coil?
Can you recommend a relay that can accommodate a very low voltage trigger?
If so, how may I modify this to trigger when put into reverse and turn off when reverse is disengaged?

Thank you for your help!

 

Welcometo AAC!

I'd try using the backup light to trigger a solid state relay or just use a MOSFET as a switch.

 

Backup light feed should go to pin 86 of the relay. Pin 85 will go to ground. Pin 30 should be brought back to battery positive, preferably at the battery positive post or the PDM. Pin 87 will be the camera input voltage. You can use a standard automotive relay (4 pin) and preferably with a suppression diode across the coil. Make sure that voltage going to 86 is 12v feed from reverse switch or bulb input. If it is lower, we will have to make alterations.

 

Welcometo AAC!

I'd try using the backup light to trigger a solid state relay or just use a MOSFET as a switch.

Thanks DL324. Ok, so try a solid state. .

Do you have any advice for voltage specifications for the solid state? My requirement is trigger to have x voltage ( any level more than zero) to turn gate on and 0 voltage to turn gate off. I am not sure what the CANBUS system does in the car so the relay might get a varying voltage when reverse in engaged.

Thanks.

 

Backup light feed should go to pin 86 of the relay. Pin 85 will go to ground. Pin 30 should be brought back to battery positive, preferably at the battery positive post or the PDM. Pin 87 will be the camera input voltage. You can use a standard automotive relay (4 pin) and preferably with a suppression diode across the coil. Make sure that voltage going to 86 is 12v feed from reverse switch or bulb input. If it is lower, we will have to make alterations.

Thanks. going to try this combo tonight. will let you know.

 

I think there is some thing going on with you car. That reverse light should have battery voltage/charging system voltage when your car is I'm reverse. I have done a few back up camera installations. VW is a bit of a pain because they use track style diagrams and you have to "decode" everything with a legend. I always hook up to the left tail lamp and run the wires down the left side of the vehicle. your left reverse light should be a black/blue wire with a brown ground. If you have a voltage supply issue on this wire that is likely your issue. Most cameras have a battery supply, ground, and the reverse on circuit. What model is your camera? You likely have a simple issue that's easily resolved.
-Jason

 

Whatever you do, do not hook into any CAN BUS wiring unless you want a nightmare on your hands. You are on the right track. Stay the course

 

Hi bwilliams60, I didn't have a diode across the relay so I think that is why this failed. I will need to source a diode to test your advice.

Hi Jasone, Thank you for the help. Yes, I think something fishy is going on. When I checked the voltage on the blue/black, I get something like 3v. But the bulb lights up fine. Oh the camera is a cheap chinese one. Only battery supply and ground available. Have any suggestions?

 

If your car is a manuel trans you have a 2 wire reverse lamp switch that provides the power for the reverse lamps. Should be on the trans.

if you have an auto you have this over though PNP (park neutral position) relay thing. That appears to be like a smart fuse box or body control module from the connector pin designation. There should be battery voltage out of pin 4 and 5 of the J226 module.

 

If your car is a manuel trans you have a 2 wire reverse lamp switch that provides the power for the reverse lamps. Should be on the trans.

if you have an auto you have this over though PNP (park neutral position) relay thing. That appears to be like a smart fuse box or body control module from the connector pin designation. There should be battery voltage out of pin 4 and 5 of the J226 module.

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Thanks, so If I can trace it here and first check why there might be a drop in voltage and fix this, it should correct things down the line.

 

Whatever you do, do not hook into any CAN BUS wiring unless you want a nightmare on your hands. You are on the right track. Stay the course

Thanks. Yes, I read it is not for normal people to touch. Hopefully as Jason says, if I can find the root cause for the voltage issue with my reverse light, this should solve the problem and your suggestion about the relay setup should tackle the rest of it.

 

Hey bwilliams60 and jasone,

Thank you for the help.

Update on this.

When I installed the camera, the dashboard alert came up saying the reverse light is faulty/burnt. What I did was I only checked the filament on the light but never thought of checking whether it was really functioning. Last Friday night, I noticed the light not working despite the filament being intact. So I tested it and it was burnt.

Then I replaced it and viola! the camera keeps turned on for the duration the reverse gear is engaged.

Well, the problem is solved but it leads to more questions: does the system know when the light it burnt, not to channel power into that circuit? Why does it do so? Time to pose a question to the Golf forum i guess.

 

Good morning Guyrat. Happy to hear that your camera is up and working. I am not all that familiar with VW platform but I do know a lot of ECM's will monitor curremt flow through a circuit or voltage to and from a circuit and can determine from that if there is a fault with the bulb. You would have to check with VW to see if that is the case, I do not knlw but I know it is possible.