Is Isopropyl Alcohol 70% a good choice for cleaning electrical wires
It might be okay, however usually we use 99% IPA, which has to be ordered from chemical suppliers (and is considered hazardous since it's quite flammable). It's usually okay to clean with water, so provided the water was pure and was allowed to dry before power was applied it might be okay to use water+IPA and a soft brush. 

Another concern is what exactly is in the remaining 30%. If it is drug-store (pharmacy) "rubbing alcohol" it may contain other additives that can leave a residue which could affect the operation of electronics. Most of the stuff available from local pharmacies here leaves a nasty white residue, and I would not suggest using it.