Yes, they are all related.
I'm more inclined to think it may be a bad hazard switch, rather than the LED modification.
There are effectively two stoplamp switches. The first one is the physical switch connected to the brake pedal, so it senses when brakes are normally applied and switches state. The signal out of this switch goes directly into the EBTCM.
Looking at the schematic for the hazard wiring. It has an internal relay which is connected to the flasher module (also contained within the hazard switch), and the output from that relay is then connected to the
output side of the pedal stoplamp switch (sent to EBTCM)...basically mimicking what the pedal switch does, but switching states electrically instead of physically.
It is done this way because you are usually not depressing the brakes when your hazard lights are flashing, so the relay function is switching the stoplight switch on and off with the the brake lights.
And it would be my guess as this is where the problem may be, since you didn't mention it occuring during normal brake application or when braking and using the turnsignals.
And yes the C1295 code does toss the "service traction system" message, because it is prohibiting the EBTCM from changing states due to this problem detected.
