Those panels are mounted in the Throttle quadrant stand (P10) left and right of the lever block.
The unit is powered by 115VAC 400Hz provided by Captain Instrument Xfer bus bus for captain and FO Instrument Xfer bus for First Officer.
The power part include 5VAC lighting, DC and chassis GND and announciators BRT/DIM and TEST
The unit features 2 potentiometers that directly act on brightness for respective ADI and EHSI displays. The EHSI one is dual concentric to control also the balance of the screen as you can state from following diagrams:
In the second picture you can note the connection between the control panel and the ADI display;
on the right you can also note the primary ARINC transmission channel which will transmit the DH set on the display as well as the range, mode and display options (ARPT,NAVAID,RTE DATA, WPT) selected on the panel.
The display mode (MAP,PLAN,VOR,ILS) is also sent out with discretes to interface to other equipemens like the VOR tuning panel as you can see in the following diagram:
The WXR display is set on as a discrete interfaced to the weather radar control panel located in the pedestal stand (P8)
Here is a video of power up test. Enjoy!