Bright and Shiny
Often the faults you'll find from voltage-drop testing will be corroded connectors — circuit killers if the condition is let go, but easy to fix once found. The usual way to clean connectors is with Scotch-brite or bronze wool pads, which work well on flat surfaces but are difficult to use on panel screws, female connectors and hard-to-reach spots. I've seen my auto mechanic go right for a can of Contact OL from Wurth. Spray it on to remove oxides, sulphide residues, oils and dirt, while leaving a protective film. He's also taught me to see if the wire itself is corroded under the insulation. If you can't expose clean strands, replace it.