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Howdy E-95,

What you have drawn will work.

I ended up doing something similar. I agree with usmcdoc14 that relay is overkill. If you have the space that is fine but I would do away with it.

You can also combine relay 4 and B into one. You can drive a single relay with two inputs following the attached schematic. Where my diagram says "Tap into wire for dome lamps" you would tap into the wire for the backup lights.

I used the capacitor across terminals 86 & 85 to eliminate pulsing when the relay is triggered by the reverse lights. I did not know if I would get pulsing from the vehicle's can bus system when triggered by the reverse wire so I added the capacitor just in case.

This is how I did my backup lights. They come on with a switch or when in reverse.



If you don't want to mess with the bridge rectifier you can use a single 1/4" watt diode as shown in this diagram.


 

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Ah, thanks MoridinTX! Much appreciated! :beer:

I'll admit, I've never done any automotive wiring so this is all new to me. Looks like I need to pull out the books and learn about capacitors and diodes. :)

E-95
Welcome!

It was a learning experience for me as well. I wish I could take credit for it, but I learned from others.

The whole can-bus was news to me. I did not realize that the signal was pulse wave modulated (PWM) and that using that to drive the relay would cause the relay to pulse. I am just passing on others knowledge :)
 

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Yea, I read something along the way about the computer using PWM to verify onboard system health. Given the resounding advice to power the rocker switches directly off the ACC or cigarette lighter, will the PWM cause any problems? Or do those circuits not utilize PWM?

E-95
The ACC is powered from the battery, not the can-bus. Running the switches from the ACC is fine. The only problem you would/may of have had is with your original design when using the relay triggered by the reverse lights.

The same goes with the design I posted when triggered by the reverse lights.
 
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