I've restored many older cars that have had harness/connector problems. I would start with a local junkyard and get yourself another ICM and as much length of the needed section of harness from the donor vehicle as you can get. I would start with just swapping your ICM with another and checking to see if that solves your problem. You can have a crack somewhere in the ICM or in its connector and thus you think your harness is bad. If that doesn't solve things then you can carefully mark the location of each wire and pin and dremel all of the plastic away so that you are just left with the individual wires and pins. You can check each pin and wire and hook them up one by one. If that works you can then inject some silicone around everything and it will be good to go. As a last resort you should cut off your harness near the connector and splice in another from a donor. Use solder and heat shrink tape on each wire. Don't cut the wires short, instead try to make your new harness longer so that you'll have less stress on the wires when you're done. Good luck!