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78 280Z overcharging problem solved.

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I was able to fix my over charging problem on my 78 280Z. Here’s my story.


My 78 280Z has been overcharging the snot out of my battery since I got it last month. At first I thought it might be the ground connections, but I cleaned them all and checked them with my ohm meter and the grounds were ok but it still overcharged (17.7 volts at the battery at idle, over 19 when driving). Well 78 is the first year that Nissan decided to go to an internal regulator, deleting the external one. So I bought a new alternator and installed it. It still over charged like mad!


Out of frustration I bought the service manual and went to the trouble shooting area for the charging circuit and it didn’t help at all.


Well the wiring on this Z has been tampered with so much that you just don’t know where things are going so at least the good wiring diagrams of the manual helped me trace the problem out.


What it finally ended up being was the wire connected to the “S†terminal of the alternator. That wire should be coming directly from the black fusible link that connects directly to the battery. If no voltage is on that circuit the regulator stays full open thinking it needs to charge full blast. I ran my trusty ohmmeter between the “S†terminal and the + side of the battery and go no reading! The last owner for whatever reason had changed the damn wiring. I ran a jumper from the “S†connector to the “B†connector on the alternator and suddenly it’s all running at 14.4 volts! Problem solved.



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