I use one of these to check the voltage/amperage under load, it shows me which cables are pulling the power down and which ones can carry the load, cheap and seems to be reliable. I eliminated several cables right away. This is just one of many on Amazon, I picked it because at the time it was on sale, but it works fine. https://smile.amazon.com/gp/product/B078SQ9HRG/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1