2008 Fx4 topper 3rd brake light

[2hand]

Working through some bugs in my 2008 Fx4. Ranch Echo topper was installed in 2012, and the photo shows how the 3rd brake light was wired into the tail light assembly at the dealer. Trying to figure out why my 3rd brake light quit working. I measured 12 volts to the main brake lamp, but only 3 volts to the 3rd brake light plug. The 3rd light worked with 12 volts on the work bench.

Does anybody know what the module is that the red arrow points to? I only read 3 volts at the lug the red wire connects to. The red/black pair go to the 3rd light.

Thanks!
2hand

 

[SenorNoob]

Surely not but that looks suspiciously like a small engine rectifier.

Bridge Rectifier, 20A, WILDFIRE KBPC3510 Wildfire Generator Parts (WF-KBPC2010)

KBPC2010 Wildfire Equipment Other Generator Parts WF-KBPC2010 - Bridge Rectifier, 20A, WILDFIRE KBPC3510 Wildfire Generator Parts

www.smallenginewarehouse.com

 

[Uncle Gump]

It a lamp module...

It sorts out the left and right commands and only illuminates the third brake light when brakes a applied. It's necessary because your brake and turn bulbs operate on the same circuits.

 

[2hand]

It a lamp module...

It sorts out the left and right commands and only illuminates the third brake light when brakes an applied. It's necessary because your brake and turn bulbs operate on the same circuits.

Aaahh. Thanks! Got any idea why I only have 3 volts on the red wire lug?

Cheers!
2hand

 

[Uncle Gump]

I would first look at the scotch locks on the wire. Those corrode... and create resistance. If all good... it likely the module.

 

[Jim Oaks]

You can find those Logic Modules on Amazon for around $20.

The one below is actually called Truck Cap 3rd Brake Light Logic Module for Camper Shell/Truck Topper

 

[pjtoledo]

monitor it while the lights are working.
possible a bad ground creating a voltage divider circuit.
getting power to a device also requires getting that power back to ground.
it looks like a rectifier because that's basically what it is.
keeps one side of the turn signal from back feeding the other side.

 

[2hand]

I would first look at the scotch locks on the wire. Those corrode... and create resistance. If all good... it likely the module.

Those diodes used in rectifiers are a pretty hardy breed, so I lean towards a bad ground dropping the volts. Unfortunately, the tech that installed this didn’t leave much wire to work with on the back of the lamp socket. I’ll most likely have to splice some wire in and create solder joints where the suitcase splices are and cover it all up good with heat shrink.

 

[2hand]

You can find those Logic Modules on Amazon for around $20.

The one below is actually called Truck Cap 3rd Brake Light Logic Module for Camper Shell/Truck Topper

View attachment 135644​

Thanks for the link, Jim! Very much appreciate it.

 

[tinman_72]

I would first look at the scotch locks on the wire. Those corrode... and create resistance. If all good... it likely the module.

I second that. There is no protection from the elements. I would replace those first. At least with butt connectors and heat shrink around them. Solder and heat shrink is even better.