Is there any method to clean the end of multi stranded copper cable that has gone black with corrosion when you can't just cut it back ?

This is to repair connections on old devices, tools, power leads, appliances ect either by crimping or soldering , I'm thinking an acid dip or specific type of flux ?

 

Try dipping in vinegar a few minutes and after, in baking soda solution to neutralize the acid and rinse. Come back with your results.

 

I have had a bit of luck sometimes with mechanically scraping off some of the black. And at one time I had a roll of RADIO SHACK brand solder that would work on wires that were brown, not black yet. So some non-acid solder flux types work a lot better than other types.