[davepl]

409 is great, Fantastik is good, and even GoJo hand cleaner works well for getting grease and grime off of wiring harnesses.

I've take the whole harness into the laundry sink and soaked it in Tide and then cleaned it to like new, but there's always a risk of water damage/rust/oxidation in the connectors when you do that. I blew it all out with compressed air fairly diligently though and no problems to date.