Couple things I have used are...
If there is paint overspray on wires you can scape off gently with a sharp pocket knife.
To clean them, goo gone works well and hand cleaner works without harming the wires.
Jeff
I'll tell you the best thing I have found after trying all sorts of cleaning agents and degreasers, soda blasting. That's right! just make sure it is out of the vehicle. Not only does it remove all the gunk, tar, overspray and other items but it leaves everything looking new. I tried it on the trunk light harness with the "cloth" wrap around the wire.....wrap had overspray, many years of black gunk on it and all sorts of other items. After soda blasting, it looks brand new, even the "cloth" wrap around the wire.
Soda blasting also works great on all those painted or plastic parts, such as rear taillight assemblies, and marker lights (backside of these). It cleans off everything and simply leaves them looking like they came from the factory. The best thing about it is it is super easy and no scrubbing or letting parts soak or 2-3 cleanings and no smearing on the plastics either. Honestly, it has done wonders for me.
BDK