So my wife was following me to the tire store the other day and said the upper left and lower right stop lights on my F150 were not working. Each tail light has two 3157 dual filament bulbs plus the backup light. Both 3157 bulbs light up for the regular tail lights, but only one activates for the turn/stop light. Seems like both should. The power for both of the regular tail lights are fed from one source, the stop/turn signal portion of the bulbs is fed separately for both bulbs. It's appears that the one power source is dead for some reason.
Thanks.