I have read a little (very little) on canbus and have a general idea on how it works. For lighting, I get the impression that if the current draw is "out of spec" you will get an error code. My question is this. I want to tap into the back up light circuit and add about 1.6 additional watt draw. On my parking lights I want to tap in and add about 1 watt additional draw, both via small led lights to increase visibility. I asked the service manager at a Ford dealer if there would be a problem and he felt there would not. He stated most problems he sees is because of poor installation, corrosion etc. I solder and heat shrink everything so that should not be a concern. My question is from a light circuit perspective what will mess up the canbus?

 

The buss network is just that, a communication network between the computer systems on the truck. When it gets down to the end where the rubber meets the road and the lights are powered, I don't think the network will be affected.

If you are still concerned or want to put larger lights/loads on these circuits, go buy a bosch type relay. Let the truck's original circuit drive the coil of the relay, which will be a very very small load. Then you can tap into power where ever you would like, run your own fuse and run that new circuit through the relay to your new lights. If you did have a wiring problem with your circuit, it would blow your new fuse and not affect any of the original lighting or truck fuses.

 

CAN-BUS (https://en.wikipedia.org/wiki/CAN_bus) has nothing to do with your lighting or your proposed modification.