Michael, if I was you, I would leave the vacuum alone and NOT rewire it so the powerhead shuts off when you shut off the vacuum. Remember - Aerus intentionally manufactured the Ultralux this way, for a specific purpose, so that the DriLux powerhead could be used with it for dry carpet cleaning with Capture carpet cleaning powder. If you rewire the vacuum so the powerhead shuts off with the canister on/off switch, you're removing a "feature". And with it, part of what makes it "unique", and possibly a sought-after model in the future that makes it more valuable & collectible. If you ever decide to sell it, you may regret it if removing that "feature" made your cleaner less desirable to a collector, and less valuable. And you can live with it by simply shutting off the powerhead separately, not a big deal.
I would look into getting the lights fixed though. It's not electronic, it's all solid state stuff inside. The Aerus Lux Legacy is still made with the lighted control panel, chances are it's a easy fix.