Originally, I thought that the bulb was just blown out...had some time over the weekend to finally check it out.

First, I simply replaced the bulb and it worked for a minute. Then I assembled the light housing and shut the door. Then, tried it again.....nothing!

So, went though the whole thing again. Worked, then not work...!!!

I then tested for continuity on all sides, bulb included, all good. Still, nothing....

Then, I check the voltage readings. I measured 10.83v...? I am just wondering if the bulbs for the upper brake light should be a lower voltage one? If not, and the voltage should be at 12v's, then it seems there is a grounding or other wiring issue.......

 

If your reading is with the bulb in-place, and "glowing", then there is series resistance somewhere (bad connection, corrosion, cold solder joint, etc.) that is providing the voltage drop. If you remove the bulb, voltage reading should go up to almost battery voltage. If it does not, with both brake lights out, then you begin to look for slight grounds on the system. And voltage drops add up, so a little on the battery terminal, the main underhood fuse link, the attachment wires, the frame ground, the ground point for the rear lights, they all add together. Considering that with truck running, you should be starting with about 14.2 volts at the battery, over 3 volts of drop will make for wimpy lights.

 

Ahhh......I recall removing some wires that was used for a subwoofer. Let me pull the seat out and the panel to see what is going on (). I think the ground connect is in the same spot...probably an exposed wire.

Just glad that the drain is insignificant to kill the battery....and that it is only isolated to the top brake light mounted on the back glass.