Cockpit Panel Lighting

Last Updated on February 5, 2026

Background

On the real Boeing 737NG, only certain cockpit panels are powered/back-lit when the aircraft is on battery power (DC power). When AC power comes on line, the rest of the cockpit panels and lights come on. This is done to reduce the power drain on the batteries, and power only the most critical components in the event of an AC power failure.

I replicated this functionality in my sim, but always had a hard time remembering the panels that come for each bus, so I created this diagram to jog my memory. I hope it also helps you more realistically simulate cockpit lighting in the NG.

Cockpit Panel Lighting by Power Bus

The left side of the diagram below lists all the panels powered by the DC battery bus. The right side shows all the remaining panels that turn on when the aircraft switches to the AC bus.

Wiring the Relays and Panels

I use a Phidgets 4x relays in each major panel section (FWD OH, AFT OH, Pedestal, etc). This enables me to turn on/off each panel’s backlighting depending on the currently powered electrical bus.

I wired one of the 4 relay outputs (let’s call it RELAY1) to the section’s DC-bussed panels. Then, I wired the second of the 4 relay outputs (let’s call it RELAY2) to the AC-bussed panels in the section.

Finally, I used 5V DC power for input power to the relays (typical backlighting power).

Software Configuration

Within ProSim, I use the AC and DC power bus “Gates” to assign all of the appropriate Phidget relay outputs to. I have highlighted the gates to use in the screenshot below. The settings below can be found in the ProsimB738 Combined Config screen.

Functionality

The ProSim DC bus “Gate” becomes active when the aircraft is on battery power (the DC bus). This, in turn, activates all the RELAY1’s, lighting the panels on the left side of the diagram above.

When the aircraft switches to AC power, the ProSim AC bus “Gate” becomes active. and both RELAY1 and RELAY2 turn on, so all the panels become powered, per the right side of the diagram above.

Conclusion

Using the above method, you can more realistically simulate the operation of cockpit lighting in your simulator.