I have just developed a break light issue that has me stumped on my 66 300. All the back lights on the right are functional. On the left all lights work expect the break lights. The left turn signal and lights work however the left break lights don't work. I tried replacing the bulbs but have the same results. Looking for some advise. I did down load the wiring diagram but haven't tried tracing wires back . Thanks for all the replies. I found the dark green wire that runs from the turn signal switch was pinched inside the steering column. It was caught between the column and the cancelling unit.