Datsun Roadster Forum-311s.org

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?

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

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.

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