01 Montana Service Traction

Here's the scoop:

Service Traction System comes on, along with the Trac Off light.

Wife reports that also, I think when breaking, the hazards lights come on.

Also When stopped to turn left (left turn signal) it blinks faster, indicated a tial light defective.

So I have her turn the signal on while in park, Normal yellow left hand turn signal lights @ the rear. With Signal on, Break light works normally (left). With Signal one (left) Left Break light Flashes in sync with the turn signal, normal turn signal does not light up.

Everything has started happening around the same time so I think they're related.

What things should I check?

I too had similar tail light problems. It is a water infiltration problem. I pulled the tail lights from the body. Unplugged the electrical connector. Found that both the male and female ends of the electrical connector for the tail lights were burnt. Namely the middle one of the three side. Replaced the female ends (driver and passenger) with clean junkyard ends ($10) and replaced the bulb holder sockets (called circuit board) with aftermarket parts. $30 for pair.
After job was complete I broke open the circuit boards and found the connections of metal/wire extremely rusty. Probably the root cause.
Hope this helps.