I've been doing a lot of reading through posts as a guest, figured I should register and ask this before I blow money on a part that may be fine.

Both rear brake lights stopped working, third brake light still works. I do have the aftermarket LED replacement (entire housing, not just the bulbs), but they have worked fine for several months and since it's both I don't suspect them.

I have done a lot of reading on the corrosion related issues with the PDU/IMP (fusebox), and most issues seem to related to corroded traces. I have removed my PCB and there is no apparent signs of any corrosion, this has been a socal truck its whole life. What I am less clear on is when the FCM may be the problem, and if there is any way to isolate which one it is. Although I would hate to spend $200 to $400 replacing one of these that is bad, I would hate replacing a good one even more.

Any help/pointing in the right direction is appreciated, this is a 2005 Cummins 2500 quad cab.

 

Have you tested for power at the taillight. Don't know much about led lights on a dodge but I would think that a spike could screw something up. I know Harleys have a load equalizer you have to install because led's don't draw as much power as the standard bulbs. Good luck

 

I automatically assumed since both lights had gone out at the same time it had to be something upstream, especially after reading all the PDU related electrical problems people have. However once I tested the lights sure enough they were bad. The ones I bought have 2 LED modules, one for running lts/turn and one for brake. I switched the connectors and got the brake lts working, figured that was more important than turn signals. The replacement lights I got have all the necessary electronics built in, you don't need to do any external resistors etc. Ordered a new set, they will go on tonight.

 

LOL, when troubleshooting don't assume anything. If you do you will miss important information. Start at the easiest place and work in a logical step by step manner.

 

On the positive side I am now familiar with the disassembly of the PDU... what a fine piece of engineering that is.