Obviously, there's issues hooking up the dimmer feature on new head units, and Toyota's, since that's all I found searching. I have a ground wire and a hot dimmer wire on the 3rd gen. harness, and only 1 lead on the new HU. Should I just leave this thing disconnected to avoid any issues? I read these things are wired bass ackwards on our rigs. All I have is the diagram they gave me with the new Head unit. No actual schematic to speak of? Advice?

 

i just used a harness that plugs into the factory wiring been working find

 

That's what I have. But that harness has 2 wires for the dimmer and the Pioneer only has 1 comming out?

 

The main issue you run into is the stock Toyota dimming lights are set up with a floating ground. That is all the lights are powered from a common source then the "grounds" are all tied together and then run through the dimmer to finally hit ground. If you connect in a device that is grounded to the chassis (common with 1-wire lighting setups) then you find the device runs in parallel to the dimming lights and that makes it dim opposite to the rest of the lights. But if the dimmer input is just a voltage level sense , then it is probably OK to connect the hot dimmer wire from the vehicle to the dimmer input of the radio. Or just tie it to a 12 volt power line to keep it constantly dimmed.