I should be able to help you out as I just installed a pioneer double din myself last week.
Remove your dash and glove compartment:
You will need to buy 2 harnesses:
Metra 70-8113 (for ACC, constant 12v, ground and illumination purposes)
Metra 70-1761(for the 8 speaker wires and you will need to extend all of them to the glove compartment, you can use this harness for constant 12v and ground as well but there is no ACC)
Harness in the middle is the 70-8113 and the one in the glove compartment is 70-1761
Metra 70-1761 (for the 8 speaker wires which you have to extend)
Metra 70-8113 (for ACC, constant 12v, ground and illumination) - I cut the RCA wires as they are useless for me. The OEM light green wire is the illumination wire and there is NO corresponding wire on the 70-8113 side, you will need to un-pin one of the useless wire from 70-8113 and insert it back to the corresponding hole in order to get the illumination to work.