Hi,
The difference in model years changes the design of the circuit. I'm not sure what all you received with the replacement doors, so I added the wiring schematics below for both the 2003 GMC and the 1999 Chevy.
Take a look through them and let me know if they help or if you have other questions. This may end up a little more difficult than you expected. Regardless, let's see if we can get it to work.
Here is a link you may find helpful when working with the wiring:
https://www.2carpros.com/articles/how-to-check-wiring
Let me know.
Joe
See pics below. Note: Pics 1 and 2 are the schematics for the 2003 and pics 3 and 4 are for the 1999. Each schematic in my manual was only one page, but I had to cut each in half to make them readable for you. I did overlap them so you can follow from one to the next.
Let me know.
Images (Click to make bigger)
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Wednesday, March 2nd, 2022 AT 7:06 PM