Checking voltage drop isn't rocket science. Just touch the meter leads to both sides of a connection with current flowing. For instance, put one voltmeter lead to the battery post, and the other one to the cable terminal while someone spins the starter. The meter will read the fraction of a volt that is required to push the current through that particular connection. If the connection is loose or dirty, it uses up too much voltage. Several of those bad connections in series with each other use up voltage that would normally be available to run the starter. If you use a wire brush and scrub the terminals before bolting them together tightly, the resistance will be minimized. It's also possible to check for internally corroded cables, etc. by touching the voltmeter leads to both ends of the cable with current flowing. Cables should have virtually no voltage drop. If voltage loss can be measured, replace the cable.
Jerry
