Charging system gremlin

I can not tell from the photo, but that might be an early 70/ later in other words isolated field. On any alternator, whether grounded field or isolated field (70/later) you need to determine if the field is continuous, if one end is grounded if you are using a 69/ early regulator, if it is incorrectly grounded if you are using a 70 / later regulator

A quick way is to jumper power to the field terminal and in somewhat subdued light, see if you can see a small spark. Better is to hook your meter in series with the high amperage scale, and see if it draws current.

Be careful that it is not just plain shorted, as the field/ ignition/ regulator circuit is not fused

You also must be careful of rebuilds. Often guys get a 70/ later configuration when they wanted the early type, but sometimes the rebuilder grounded one field whether you wanted that or not, and WORSE, sometimes one field terminal is grounded and the rebuilder LEFT THE FLAG TERMINAL in place. This means that you can mistakenly get the VR wire (pre 70) mistakenly on the grounded terminal, or 70/ later, might by chance get the field power wire connected to the grounded terminal.

This is a simple problem, but you must check it out