There are a lot of factors in play when choosing the appropriate wire gauge for carious components on your motorcycle. Most of the charts that you find online are going to be for commercial construction applications rather than for motorcycle or automotive use. I've never come across a chart specifically for motorcycles so I made one using a calculator that factors wire gauge, amperage, and length.
Note: The length provided must be divided between the Positive and Negative lengths of wire for that circuit. For example, if the component in question has a chassis ground, the entire wire length can be applied to the Positive wire.