[68c10airstream]

Welcome aboard. Look at the battery cable ends at the battery. If they have been cut and a replacement ends put on and you can see the individual wire strands you will fight this for ever because air, battery acid vapors are getting into the cable strands and getting corroded causing voltage drop under load. Those replacement end clamps were considered "emergency clamps".

If you do replace cables watch out for china crap with fewer strands, and rock hard plastic insulation. American made standard plus brand has been very good if they are still usa sourced.

Being that you have a volt meter, your answers are a test away. Scrape the top of the posts shiny, stick one lead on say the positive post, and pierce the positive cable with the other lead just downstream from the clamp. Have somebody crank it over and read the meter. .3 volts or more equals repair. Ignore if the meter shows a - symbol next to the reading. I just means your leads are reversed from the electrical flow. Do the same at the negative post. Another test is to feel the clamps, etc, while somebody holds the key in the crank position. You may get burned, but the resistance is very warm/hot. Good luck.

To keep it easy, the test stated above makes the meter into a jumper cable because you are parallel to the cable being tested. With resistance present, it's easier for the voltage to go through the meter than through the resistance, so the reading is telling you how much is needed to boost it up to what is needed. It's called a "voltage drop test". Probably the best test i learned for electrical repairs.