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Need some advice on a 620


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I have recently been having issues charging my truck. After replacement of battery, reg, and alt, I also moved the alt to the other side of the engine bay to get full use of the belt with a larger alt. Currently on the alt the terminal marked bat goes to a white with red stripe, terminal marked E goes to a black wire, the two male connections are the top score is going to white or yellow with a black stripe and the vertical plug goes to a solid yellow.


With that said, sometimes when I go to my truck in the am it's sitting at 11.3-11.8vdc other times its between 5-7vdc and needing a jump. When I drive I sit at a expected charge.

If I swap the two male plugs, I over charge while driving or maintain without charging, but I don't depleted when parked.

Nothing is left on and the only other odd thing happening is my oil light stays on dim when driving.



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Could be a bad ground or a short. 


Turn everything off in the truck. Disconnect the negative cable and put a test light between the post and the cable end. If it comes on you still have something drawing power. You can pull fuses until the light goes out to find the circuit that is still on. 

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First I have to say throwing parts at a problem is not only expensive, but you risk replacing a good part with a bad (and inferior quality) part. Hope you kept all the original parts for spares. Most are better than the new ones. For example a replacement alternator is around $250


Second you say a you replaced with larger alternator. Larger as in physically larger? or higher output. Higher output alternators are generally from later models and are internally regulated. Your '77 was the last year that Datsun use external regulators and an internally regulated alternator will not work on that system. The system can be modified though. What alternator did you replace your old one with????


Third. A fully charged battery with the engine off is 12.7 volts. Can be as low as 12.4 if very cold. An 11.3 volt reading is under 10% charged. So battery is not charged up for whatever reason. What does it read running? should be over 14 volts.

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Hey Mike good to hear from you.

The original parts have been changed for some time. Everything but the battery was a warranty item but still had to put money up and cover shipping to store.


The alternator I had in was a larger output as well as in size. I want to say the current one is supposed to be pushing around 60 amps vs the original 35.


When driving the voltage will range from 12.8 to 14.6

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Do you know what the alternator is out of? The year?


If an Hitachi it may be an original and have a foil label on it? If it says LR anywhere it is a later internally regulated unit and your system won't work properly with it.

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if low reaL LOW VOLTAGE AT IDLE WITH EVERYTHINGOFF. THEN WORK ok higher rpm is good indication but say put light on with higher rmp and get low voltage I say brushes goiing bad.


but a wondering voltage to me is the wrong alternator in there


If you have a iNTERNAL reg alternator then pull the external one and add the jumper wires. to convert to run a IE type alt

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