hi
#2
Yes it is a bad ground. Since it is happening when the brakes are pushed, then it must be in the rear. If you have problems when you turn the headlights on, then it is in the front lights.
Take the rear brake/turn bulbs out. 99% of the time, the brass part of the bulb is not making good contact with the little tang in the side of the plastic socket. Sometimes just wiggling the bulb around will fix it. A little fine sandpaper or steal wool on the outside of the bulb should shine it up, and a screwdriver can be used to scrape the tangs in the socket.
If this doesn't fix it, then I would investigate the black ground wire leaving the socket. See if it is in good shape, and is not corroded where it hooks to the body.
Take the rear brake/turn bulbs out. 99% of the time, the brass part of the bulb is not making good contact with the little tang in the side of the plastic socket. Sometimes just wiggling the bulb around will fix it. A little fine sandpaper or steal wool on the outside of the bulb should shine it up, and a screwdriver can be used to scrape the tangs in the socket.
If this doesn't fix it, then I would investigate the black ground wire leaving the socket. See if it is in good shape, and is not corroded where it hooks to the body.