Tow Mirror Cargo Light Wiring Help

[99Wildcat]

Just upgraded the mirrors on my 1999 K3500 to the 2015 style. The power mirror harness was plug and play and the signal and marker light wiring was seamless. These mirrors have separate leds for the signal and marker so I didn't need to modify anything. I chose to wire the cargo lights on the mirrors to come on with the cargo light switch. I back out of the shop with one mirror folded in, so I don't want the lights coming on with my reverse lights. I spliced into power on the dark blue and white wire near connector 298 under the column. According to my manual, this is the cargo light feed wire coming from the cargo light switch. I grounded the mirrors individually in the toe-kick areas. Everything works great with one exception. Instead of the courtesy lights shutting off 25 seconds after shutting the doors, they stay on and the mirror cargo lights turn on (although all lights are dimmer than normal). Once I open the door, the courtesy lights come on full bright and the mirror cargo lights shut off. The truck cargo light functions normally. Turning the cargo light switch on does make the mirror lights brighter. Somehow the lights are getting back-fed power I assume. The manual states the cargo light circuit gets its ground from three or so different places. Do I need to ground to the same sources? I can't make sense of it. I have the courtesy fuse (3) pulled to keep from draining the battery. There were no electrical issues prior to the mirror install. Any help would be greatly appreciated!

1999 K3500
7.4 4l80e
CCSB DRW
"Conversion Vehicle"

 

[99Wildcat]

Figured it out with the help of this thread!

https://www.gmt400.com/threads/cargo-light.35520/

If the cargo light switch is on, for the light to work the cargo light circuit must be completed by applying ground in one of three different ways. Ground is applied by the courtesy lamp switch (dimmer all the way up), via a remote lock receiver, or the interior lamp control module. This is the module that keeps ground applied for 25 seconds after the doors are shut then turns the courtesy lights off by breaking the ground.
When I grounded the mirrors to constant ground I provided a path for current to flow through one of the three devices which lit up the courtesy lights and the cargo lights in the mirrors.
I prefer to have the cargo light circuit separate from the courtesy lights so I don't have to turn the courtesy lights on to use the cargo lights. The way it is set up now, the cargo lights will stay on as long as I need them to or until the battery dies. There is no module shutting the cargo lights off 25 seconds after I shut the doors.
To isolate the circuit I slightly modified the wiring behind the Cargo High Mount Stop Lamp. It is a 4 pin connector. The brake lights use a white wire for positive (mine was off-white) and a black wire for ground. The cargo lamp uses a dark blue-white wire for positive and a white wire for the controlled ground. I cut the controlled ground (white wire) and spliced the pig tail coming out of the connector into the chassis ground (black wire) so that the brake lights and cargo light will both have a chassis ground. I secured the loose end of the white wire going into the cab with electrical tape because if it grounds out current will flow through one of the three controlling devices, power the courtesy lights and drain the battery.
Hope this helps!