I know what I did, I know what the trouble is, and I don't know how to fix it. I know that wiring diagram would help, and my knowing how to read a wiring diagram would help even more so.

Here's the thing. On my '93 GMC Sierra, I pulled away from my boat trailer, and failed to unhook my lights. It did some interesting things to my wiring to all my rear lights.

But first, some years ago, I had to pull the fuel tank, looking for a short. In doing so, I spliced in new wiring over the fuel tank area. So now, here's what I've got after two weeks of laying under that truck, wiring and rewiring...1) Brake lights work. 2) both signal lights work. (3 flashers work), 4) back up light works. 5) tail lights work.

BUT...When I turn my left turn signal on, and have any other lights working or on, or when I hit my brake, the left turn (in the rear only) does not work. It simply remains lit on both the dash and the light itself. In short (forgive the pun), I more or less delete my brake lights when using my left turn signal.

I'd like to know where the yellow wires run, and the brown wires, and how is it that both tail/signal and brake lights use the wire...or where do they crossover from one to the other? All the right side lights work just fine. I've replaced several wires from the firewall, all the way back...and I'm convinced I've mismanaged the yellow wire up, and/or the brown.

 

Well, I figured it out on my own. Wiring diagrams and those who claim to know indicated that somewhere in the brake light/signal light circuit a connection allows the signal light to serve as the brake light, by simply causing the signal light to remain on when hitting the brake.

In my case, I had turn signals until I hit the brake light, then no lights on that side of the truck. So, I knew I had brake light wire, but simply could not find where it joined the circuit.

So I removed the brake fixtures, and drilled a 1 inch hole in the web of both rear light fixtures, in which the other bulbs were installed. I then added a$1.99 light socket from Auto Zone, into each fixture, and ran the brake light wire, straight to them. I now have, instead of four bulbs in each rear light assembly, five. The new brake light bulb lies between the two large bulbs.

You cannot tell by looking, that anything has been altered, for everything I did was interior to the light fixtures. And the fix works perfectly.

I never got a reply to my question...and so found very little of use on this forum. I hope someone with a similar problem can gain some useful knowledge from this post.

Julabee Jones