Your multi meter won't help you diagnose a main cable problem as it doesn't have the "nerve".

Basic check is to turn on the headlights and see how they look. If they are dim, you either have a dead battery or there is resistance at connections. Pull and clean the terminals completely and clean the battery posts. Reassemble with dielectric grease and smear some all over the connectors and posts too.

If this doesn't help, next step is to check the positive connector and cable to the starter. It's hard to see, not because of it's position, but because it is obscured by intake plumbing etc. Don't attempt to service it without disconnecting the battery again. Also check the small connector(s) just for good measure. Make sure that battery cable is clean and tight. Make sure the post is not all corroded, fasteners clean, etc. There is usually a water tight boot on the hot terminal. However if anything has been done down there, it could be askew or missing.

Next, trace the ground terminal to the block. It should attach where the AC/PS bracket bolts to the block. Clean? Tight? Of course also check where each of the power cables attaches to the appropriate lug/terminal at its end.

If all of your primary supply connections are good, you can "hot wire" the starter to see if it's good. There are two terminals on the starter solenoid. remove the connector on the one furthest from the block. Should be a blue/yellow wire. If you jump this to the battery terminal with a screwdriver and the starter/solenoid is good, the engine should crank. If not, you found your problem. If it does crank, then your ignition switch would be the next stop. The terminal blocks on the ignition switches are a known weak point. If you have any other ignition controlled accessories that are also giving you problems intermittently, then the switch block should be changed from behind the key switch, under the dash.

DS