volt gage reading??

[74 dustaar]

At an idle my volt gage reads to the negative a bit but when I increase the idle the volt reading goes positive, am I not charging correctly? Belt is tight and no slipping.

 

[RedFish]

Could be a bad diode in the altenater. Part store can check it for you. I've seen many slant 6 cars driven for years with a weak charging system. Headlights blare up on acceleration. Those cars didn't rust as fast as others either.