[-=Jeff=-]

This is from an 88, probably the same in later years but maybe not

GM used the filaments of the bulbs to their advantage, if I apply 12v to both sides of the bulb it will be off, but with LEDs that does not work, since the Bulb is basically a short, the new LEDs are not.

IF I were to place the LED in the front of my car and remove the front Side marker it will work in both cases

I have a 2 relay (per side) solution which might be the best I am going to get. it will change the wiring of the marker light and a ground will need to be added, But it would work.

Also in current OEM state, if you put LEDs in the front side marker, they will only with parking lights OR Turn signals, not both ( due to GM Design)