Hoping someone can help me here with a head scratching issue. Working on a 2006 Silverado 3500 diesel. The truck has been converted to a flat bed prior to me owning it, and has LED lights. I lost all my rear lights recently, including flat bed side lights, and headache rack lights. Literally all rear lights. I knew I must have a corroded or broken wire for them to all go out while driving, and were flickering off and on for a week. After inspecting all wiring in the rear, found several corroded wires and connectors. So I fixed wires and put everything back the way it was. All rear lights now work as normal, other than brakes. So I immediately thought of the pedal brake switch. I own another 2006 Silverado that uses the same switch, so I swapped them out, as I know the other works. Still no brake lights. HERE IS THE CONFUSING PART. I used a test light to see if there was constant power on the orange wire at the switch plug. The answer is yes, but was only about 7 volts. (other truck shows 12-13 volts) When I press the pedal, I get ZERO power from the white wire, which should light up. I have ZERO power on the STOP fuse at the interior fuse box. I have 12 volts of power on each leg of the 25 amp fuse under the hood for brake lights. How is this possible? If power is going in to the brake switch, how is it not coming out when pressing pedal? And the switch is definitely good, as I took it back to the other truck to confirm. Can someone please shine some light on this issue? Thank you!

 

7 volts? My first thought is you have a bad ground somewhere.

 

That was my thought as well. But I finally figured it out! The fuse under the hood was testing good but it wasn't. It was working, but 12 volts wasn't passing thru it. There was a bad spot in the fuse, causing voltage drop. So technically it wasn't blown, just bad. Hours and hours of trying to figure this out, and I am mad at myself for not replacing that fuse. I just tested both sides with a test light, and didn't pay attention to voltage. That's 100% on me! But first time having a fuse do that. Lesson learned!

 

Interesting. I'm aware that fuses, as they age, can build up oxidation and just in general, fatigue leading to a drop in capacity to pass current. This is why older vehicles generally have issues with their ECU's (as was the discovery with 99-04 Jeep Grand Cherokees, at minimum, after much testing, debugging and eventual conclusion). So when I obtain an older vehicle, I get to replacing every fuse with a new one, bad or not. Glad you found the issue and even further, coming back to report your findings.