The harness will plug into the bulkhead.You shouldn't have to remove the pass. side inner or outer fender.Unplug harness from ecm and heater controls.From inside the car cut the rubber grommet on the fire wall at 12 oclock position until you can pull grommet out of firewall,once free cut grommet off harness,leave grommet intact enough so you can silicone it back together and reuse unless you have another.When feeding the harness through the hole in the firewall you may have to pull one plug through at a time,the hole isn't very big,this is while removing and installing.When you get harness free feed all plugs through hole and pull harness out from under the hood.There may be a few clips holding harness to plastic inner fender,just break them.To install harness feed a stiff wire from inside the car up through the hole until it comes out under the heater box on top of the inner fender.Tape plugs and wrap the wire you fed up through around the connectors and from inside the car pull the stiff wire back through the fire wall feeding the harness down in.Silicone grommet after even the hole where the wires pass through.Look at Pic's of my Buicks below,I did this to an 85.
