When checking grounds, items mounted in plastic, such as lights have ground wires, and therefore grounding points. Items that only have a power wire going to them obtain their ground through contact with the engine or body.

On a car of your's age, you should consider unplugging wires, cleaning the contacts, adding dielectric grease and zip tying any that you can.

Bad connections can drive you crazy!

Do one connector each week - that way if you have a problem, you know where to look.