I used the GM parts and they were easy once figured out.
You will need both harnesses as they work as one unit once connected.
under dash harness
One end plugs into the stock switch
two plugs go directly into fusebox under dash,
Attach the relay body under dash and drill a hole in firewall to pass wire into engine compartment.
Wire comes with boot to seal against the weather
Second harness (under hood harness) connects to the wire that comes from inside, a ground lug on drivers side fender. unplug low beam headlight and plug one end into headlight and other end into the wire you just disconnected from the low beam headlight.
final two connectors are for the fog lights.
Take a pic of fusebox under dash and I'll show you where the harness plugs in.
You need to verify that you have a male pin in position one of the two position connector (illumination) otherwise you have to splice into another harness to get this.
What year is your ride?
Tbruz
I