Dash Light Dimming

[CRJ AME]

So has anyone figured out how the dash light dimming system actually works? I am adding heated seats and want to have the switches internally lit. according to the wiring diagram, both sides of the dash light circuits go to the BCM. I went out the vehicle and metered out the wiring for the lighting circuit. One side always has 12 V all the time regardless of brightness setting. the other side has millivolts at full brite and 12 V at full dim. Are they varrying the ground resistance to manipulate the brightness setting? Anyone have an idea on how I can tap into this so I can internally dim the seat switches.

[CRJ AME]

Update, so they are definitely manipulating the ground side of the circuit. The glove box light and rear heat controls back lighting do not dim with the dash lights. I will have to wait until I get the kit I guess and see how the lighting works on the switch. Hopefully the are not internally grounded.

[smj999smj]

All 12v light dimming systems work by varying the resistance to ground. Any completed 12v circuit should have 12v on the input side of the circuit to the "load" or "motor" and there should be nominal voltage (almost, but not quite 0 volts) on the ground side of the circuit. It's basic electricity 101. The BCM just does the varying of resistance to ground internally rather than have a separate dimmer do the job externally.