The lighter color plug single wire...
I believe should go to your brake proportioning valve down on the frame kinda right below the power booster. If that is disconnected I would expect your BRAKE dash light to be illuminated because it thinks there is a problem with your brake system. I checked my car this afternoon and my proportioning valve had a plug like that, but not sure if the one pictured is for the brake valve or not.
Good luck,
Jerry jr