hectik

I've recently replaced the selector switch again, checked grounds, plugs. Today I replaced the encoder motor, and I still have no lights. I've ran out of ideas. Any help is appreciated

I've got a 1999 Sierra automatic, I have no lights on my 4x4 selector switches, here's the weird part, when it snows, my selector lights all flash, and when I'm driving the truck acts like it wants to stall and almost like the lights dim. this only happens when I'm in drive. they flash when in park also, and one time after flashing for a few minutes the selector switch actually worked and I was able to shift into 4lo/4auto, and back into 2hi. its only worked that only time though. I've already replaced my switch, checked the ground under the truck by the driver side, and checked fuses. before I buy any other parts, I'm wondering if you can help me out figuring this out. all help is appreciated. thank you all.