The turn signal circuit in the gen 5 tails probably has a resistance that is much lower than the BCM is expecting even when set to "LED" so that is triggering the light out DTC and this will vary between years as some are more sensitive than others. Does the gen 5 taillight still flash when the DTC is active or is the BCM disabling the output completely on error? One solution may be to wire a resistor in parallel with the light and that should get rid of the DTCs.
There may be a way to disable DTCs for rear lights altogether somewhere in the BCM. I thought I saw mentions of it in one of the up-fitter guides.
On another note, I would be really temped to wire in the CAN-IHS lines and see if the blind spot monitoring could be enabled. Looking at the BCM and comparing it to Jeep GC (almost identical BCM and options) I think these are the settings that need to be turned on.
Vehicle Config Customer Settings Menu 1:
-Blind spot alert customer settings menu: Not set
Doors Configuration:
-Blindspot Mirror Present: Not set (not needed as the chime should still work, but theres a chance the new HD mirrors would fit)
Programmed ECUs: Cabin Network:
-RBSS Right Blind-Spot Sensor: Not set
-LBSS Left Blind-Spot Sensor : Not set
@Mpgrimm2 and
@DeereGuy, thoughts on making adapter harnesses for these lights?