You have proven that there is power to end of wire. That's good. I do not know what this means
"Checked resistance from the tail light assembly wire to the terminal inside the bulb socket and the meter pegged." I think you have checked that power "would be there" BUT You must prove that there is power to the brake socket's inside center contact While power is on.
If you do have power there: (some of this is just reiterating what Rusty Rod said)
1. Be sure you have the correct bulb and that it's center tap is touching the socket contact.
2. If it's the correct bulb and is touching, you have proven the ground path is interrupted.
3. With bulb out, check continuity of socket shell to chassis ground. THIS MUST be confirmed.*see below.
3. I assume you have a separate brake light and tail light. If tail light works. Install a test ground wire from tail assy clean metal to brake assy clean metal. Bulb has to light then. You can actually touch the bulb case, while it is installed, with a test wire probe to provide an alternate test ground to chassis or a known good ground.
Never, ever assume this in any wiring troubleshoot: "Wouldn't the housing be grounded through the bolts that attach the light housing to the truck?"
The number one cause with lighting troubles is GROUND. Paint, loose screws, loose assy, rust, corrosion, oxidation.... all cause loss of ground.
* Do a continuity test from socket to light housing, light housing to brackets, brackets to truck chassis, truck chassis to neg battery post.
If you can not figure out why assy is not grounded after checking and cleaning and tightening. Add a permanent ground wire from assy clean metal spot to chassis clean metal spot.
Last edited by Rusty Rod; 01/30/2017 4:26 AM.
