One nice thing that bears repeating about using the factory harness is that all the right connectors are there. Even if you need to replace it that old connector probably has a part number on it to help you find another and it definitely is a physical example of what you need.

Unlike universal kits with universal (GM) connectors you know what you have fits.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.