Brake/turn signal issue

[Lambchop76]

I have an 87 Silverado R10 and my left rear blinker and brake light no longer work. I replaced the bulbs and sockets with the LED conversion from LMC a year ago. Everything worked great up until 2 weeks ago. I have chased and stabbed wires with a test light all the way to the column and there doesn't seem to be power to the yellow wire for that light. Could my problem be in the column in the signal switch? The left front blinker works fine though. I am completely stumped and aggravated. Any insight is greatly appreciated