Plug to Headlight switch

I continued with cleaning up behind the cluster. What a mess. The fuse box is a disaster- Only one fuse was sized correctly, 4 of the 5 fuses that were suppose to be 20A fuses were actually 30 amp fuses. The other 20 amp fuses had a 3 amp fuse in it. The final fuse that was suppose to have a 3 amp fuse in it, actually had a 3 amp fuses in it. There were wires to the fuses that were cut an taped. I think there was a fuse or two jerry rigged into the back of the fuse box.
The corrosion is terrible, not sure if I should try and clean it.