CRP_Dakota

Hello Everyone! I'm hoping someone can point me in the right direction. I've been helping a buddy with his RB25 swapped 1975 280z. However, I've ran into quite an issue. As the title suggests the ammeter is pinned at at "60+" and the wiring for shunt is getting very hot; hot enough to cause the plug to start smoking. It only seemed to have that issue after revving the car to 3k RPM. Before hitting 3k the ammeter was reading in the middle of the gauge and the wiring was cool to the touch. As soon as the car revs to 3k though the ammeter is pinned and the wiring gets hot and will remain hot until shutting the car off. It also appears that the alternator isn't charging the battery until hitting 3k rpm. Before 3k the voltage at the battery is 10.5 to 11, but after revving to 3 the voltage at the battery is 13.5 to 14. I thought it might have been an issue with the alternator since it got wet while flushing the coolant system, so that was replaced with an alternator for a 1989-1994 240SX. Specifically this one found at O'Reilly's: https://www.oreillyauto.com/detail/b/ultima-4536/charging---starting-16772/alternator-11425/f7cab2ae3cc0/ultima-80-amp-alternator-remanufactured/r110645a/4602302/1993/nissan/240sx?manufacturer=true&pos=0. This is the exact same alternator that was on the car previously. However, the issue persist even after swapping the alternator. I then thought maybe it was an issue with the external voltage regulator bypass so I rewired it. After rewiring it the ammeter was pinned and the wires got hot as soon as the car fired up. I also tried installing an external voltage regulator just to be safe and see if maybe that was the issue. However, once again it seemed fine until revving it to 3k rpm. So now I'm pretty stuck and not quite sure what to check next. I'm hoping someone on here might have experienced something similar so that they can point me in the right direction. I'm open to all suggestions and ideas. As I said I'm pretty much out of ideas as to what it could be. Thanks so much!