It gets simper than that. If you have separate rear bulbs on the rear; one for brake light and a different one for turn signal, then the signal switch is not involved with the brake light circuit. Instead, all three brake lights, left, right, and center, are all tied together. All will normally be fed right from the brake light switch, so if one works, they all should work. When just two don't work, I'd start by looking in the back for the splice where the wire to the left and right light branch off.
It is also possible for a light to have a bad ground and make just that one dead while the others work okay. There's two problems with this thought. First, you'd have to have two bad grounds for two dead lights, unless they are tied together and share a ground, but each brake light and each turn signal bulb typically also have a separate tail light built in, and those share the same grounds. Bad grounds would be a good suspect if the tail lights were also dead.
I don't think a computer is involved with the brake lights, but the engineers are insane and have seen fit to involve computers in every other circuit where they are not needed. Before you replace a computer, check all the fuses inside and under the hood. On most cars today there is a fuse for every circuit, instead of how they used to group many circuits together in the past. Also, those fuses are very likely not labelled as "Brake light". It's common now to find designations that no one can clearly understand, like "AL3", and "Comp WSP". If you are lucky enough to find one or two blown fuses, my first question would be if you had tried connecting a trailer wiring harness.
Sunday, November 6th, 2016 AT 7:34 PM