Radio problem

I have 84 cutlass supreme brougham. I can be driving and speakers will quit except for right front, then in a little bit they will come back on. I am not sure if I have a ground problem or speaker problem or possibly radio bad. Not sure how to test. I think I may be able to set my vom meter on continuity and test wires to speaker, but not sure if it has to be unplugged from radio. Don't know how to test speakers. Thanks for any help