turn signals and brake lights go nuts

I have a '05 Yukon that has an intermitten problem with the lights. The turn signals flash rapidly and dim with no brake lights. When all the lights are turned on, and the turn signals are activated, all the rear lights (marker, turn, license plate, back up lights) are dim and flash rapidly. The dealer can't find any problem.

I think problems of this nature are usually related to the multifunction switch (turn signal lever.) Everything you have mentioned is controlled in some way by this switch.

Thank you for your advise. The dealer has my Yukon again, they say the problem is in the rear module. We will see.