Where is the green wire on an '03?
I got a different cap and it has the 3rd brake light in addition to the dome light and I want it to function correctly.
My truck doesn't have a factory tow package, will it still have the green wire?

I have looked at the main harness on the frame rail inboard of the left rear wheel and all I saw is a green wire with orange stripe, but it was connected so I'm pretty sure that isn't it.

 

So your trying to wire up the high mount brake light on your shell, that is supposed to operate with both brake and cargo light?

Only suggestion I can make is tying into the wires from the brake and cargo lights on the original high mount.

 

No.
My bad.
I wasn't clear.
My old shell only had a dome light.
My new (to me) shell has a dome light in addition to the 3rd brake light which my old one did not have.
Thanks anyway for your creative suggestion.

I only wanted to know where to locate the green wire.
I have found it already, on top of the left frame rail at the very back.
The posts I found when I searched led me to believe that I might not have the green wire since I don't have a tow package. And I also misunderstood where it is located on this model which is why I missed it before.

My green wire had green tape around it where it was fastened doubled back onto the harness.

I also found out all the bulbs are burned out back there.
So this is a task for another day.