Bachmann Derby Lightweight: Why does it fail to ABC brake?

What did Bachmann do wrong on the Derby Lightweight PCB which means ABC doesn't work properly? If you want to design your own PCBs and have them made, check out PCBWay! https://pcbway.com/g/4z4dro

00:00 - The problem
00:47 - Power car disassembly
01:56 - Decoding the factory PCB
04:00 - Unbalanced power draw
04:41 - Wiring the lights to AUX1
06:30 - Power car reassembly
06:41 - Trailer car lights: the 6 pin decoder problem
07:50 - Make a 6 to 8 pin decoder converter with PCBWay?
09:47 - Packaging problems
10:43 - Replace the entire floor PCB with a custom one?
11:26 - Is there a PCB from a different Bachmann DMU that could be used?
12:18 - Getting more AUX functions from a 6 pin decoder?
13:22 - Removing the resistors from the ceiling lighting board
14:27 - Testing: Lights and ABC
17:10 - Lighting balance between the cars: What to do next?