For some reason the search is not working for me so I did some search but Couldn't find anything about this in all this threads, so sorry, I did try.
I have a 2004 Fat Boy, the break lights are not working, change the bulbs, check fuses and I'm waiting for a brake switch my local Napa store will have for me today to change that too. I did test the switch with the paper clip trick, just making direct contact of the two connectors of the wire, but that didn't work, so I'm not sure if it is the switch. Also when the problem started it was when I activate the left turning light, it lights up the check engine light and the right green arrow light on the dash was very weak, at that time the running tail lights where working, all three, now just the center one works but the side ones are not, weird thing, the turning lights are working fine now, so for a recap, the back running center light and the blinkers are working, but the three brake lights are not, and also the side running lights are not working, no problem at all with the front lights.
Any suggestion will be greatly appreciated, thank you very much.

 

No answers yet but I think I found the problem, the Brake/Running/Turn Conversion Kit I think is it, I took it off and now is like original configuration, the turning lights are working just for turning and the center is working as running and brake light, so I'm on my way to the dealer to get that, I think is like $70 here in Seattle, I'll post the result later.

 

Good job. I was going to suggest taking the brake/running/turn signal module out of the circuit.

 

Yep, that was the problem, changed the module and everything is working fine again.