If you still have your old lights it is simple enough to take the wiring out and swap into the new lights.
The problem then that I think you have is that on the mk1 sierra a lot of the inner lights were fake, they had no bulb holder and/or wiring to them, the wiring merely splits off from the mainlight mainbeam feed normally, I can only assume there is a seperate live feed for the inner lights in your loom but not the headlights, that being the case swap over the looms inside the lights will sort it.
tabetha