06' Yukon Denali brake lamps inop unless engine is running?

[nxtruck]

Guys,
I'm trying to figure out if this is how these trucks are configured. Last night, I replaced the 3rd brake light on my wife's 06' Yukon Denali. When I had finished, I hit the brake pedal to check things out and found none of the brake lights working. Before I replaced the 3rd brake lamp, the two main brake lights were working. Then, I figured I'd turn the key to the run position and retry it. Still no lights. Then I decided to start the truck and retry them. When I started the truck and hit the brake pedal, they all worked.
Are these trucks wired so that the engine has to be running in order for the brake lights to work? If so, that seems strange to me that they wouldn't work with the key in and turned to the run position. Has anyone else had this happen?
Thanks in advance!