Brake Light and Turn Signal Diagnostics

[Slemmy]

Hello! '65 LWB C10 w/230.

Had no brake lights, running lights, or turn signals. Can't remember if the dash indicators were lighting up. Bought a new turn signal switch at the recommendation of my mechanic and changed it out myself. Viola! Problem solved. All lights were working great for a couple of days. Until...

Now my in-dash signal indicators will sometimes blink, other times will stay on. No brake lights, running lights, or turn signal lights on the truck. Doesn't matter if my lights are on or not.

What are my diagnostic steps here? I'm fairly certain I can rule out the turn signal switch as I just replaced it with Echlin part # ECH DL6173.

Any help is appreciated!!