If you are lucky there will be printing on the wire giving you a clue to the wire size. Alternators come in different sizes. More current the larger the wire. You can also measure the diameter of the wire (less the wire insulation) and compare with the AWG to diameter chart.
Hey... Your right.. I bet the size of the wire has something to do with the size of the connector. My original fear was finding the right connector to fit the factory plug. I might just bite the bullet, buy the one I found, put it on the end of a wire and see if it will clip into the spare factory plug I have from the old alternator.
Thank you everyone for all of your help... I have successfully installed an internal regulated alternator that I have had laying around for over 20 years into my 1965 C30 dump truck which has been experiencing charging issues for the last 6 months. First the external regulator was bad, which fried the battery, then the plug to the external regulator was causing issues, so I followed the following video to convert it... Hope this helps someone in the future...
