1600 alternator good but not charging

[sevenmilebridge]

I've finally got my 1970 1600 finished however the alternator does not charge the system. I took the alternator to a shop that rebuilds them he tested it first and found out it works fine. I have it in the car but the amp meter reads negative amps when running. The battery wire that hooks to the alternator reads 6 volts should be 12 volts. I jump the battery wire and it charges any ideas as to why i'm only getting 6 volts to the alternator?

[Bwk2000]

In my experience, that kind of voltage drop is usually caused by one of four things:

Bad alternator, battery, voltage regulator or a loose/corroded ground wire (my money is on the last one). Check all your grounds first - It costs nothing

[Jujuman]

i agree, I had the opposite, high amp readings +30 while driving. and this was a SS VR. I changed the VR and made sure the case ground of the VR was clean. Now back to normal charging and near 0 amps while driving, but I fear the battery is cooked, my monitor reads Replace.

[redroadster]

Still using the external voltage regulator? I'd pull the cap on it then
With no energizing it its on the top contacts which should give full charge ,you can put a alligator clip connecting or hold it with rub gloves see if it charges test wiring ,try a redundant neg to the alt.base, pos pulls power

A common problem of rebuilt alt.the brushes to rotor comuntator gets glazed,from a lite coating put on to protect from the copper getting corroded I remember many a datsun needed 1/2 hour driving to start to charge , then we're good