Its actually pretty easy, all you have to do is don't secure the holding clips until you have run the harness behind the center console. The wiring maybe stiff or frayed so watch out for knuckle cuts.
Order the new transistor .It is under $50 dollors. Disconnect 4p connector.
Then measure your resistence on 3 and 4. Replace it. then Test it with 12V
with jumper wire.