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zx alternator keeps frying

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So I did the zx alternator upgrade years ago and I never had problems with it before. But the other day my alternator died, so I warrantied it out and put a new one in, and 5 mins later that one fried. So I got another one, checked all my wiring. nothing is out of place, drove the car all day yesterday no issue. Today I stated the car up and let it warm up and the alternator fried again! And every time they fry a plume of smoke comes from them and a wretched smell.


So, The way I have the alternator wired is, S is constant power and L is switched power. I no longer have the factory dashboard so S is wired straight to the BAT terminal on the alt, and L is wired to my new fusebox on a 25A fuse that is switched with the key on. I know my wiring is not bad because it worked for years before. Im wondering if somewhere in the factory harness a wire has rubbed through and maybe is grounding out?


Also my ecu is powered off the same fusebox with a switch separate from the key, so when I turn the key off the engine will stay running until I turn the ecu off I think because the alt is feeding electricity back into the fusebox. It has always done this and I actually like that "feature" because I can let my car warm up in the morning without the key in so noone else can hop in and go. However every time the alternator has melted has been when I turned the key off while the car was running, It has never done that before. I have the FSM and I have looked over the wiring diagram many times. Nothing is wired incorrectly something must be grounding out I think. 

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Then get a multimeter and find the short...something is obviously at fault. Short of having a couple bad alternators in a row (which can happen) something changed or you never had it correct in the first place.


FSM isn't going to help you with fitting a 280zx alternator into an S30, find one of the excellently written guides online for the swap. 


I didn't see any mention of the voltage regulator delete was that done?


If you have a 240z or 260z then you may have to add a diode to stop the feedback loop, look for it online, you aren't the first. The L wire is supposed to excite the alternator to tell it to function, right now it is probably failing and causing a feedback loop and feeding power via the L wire. That is a lot of voltage to try and keep the car running through what I imagine is a pretty thin gauge wire. 


Fix it and take your dash out and hope you haven't melted any of the switching blocks.

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You can't wire the "L" directly to the switched voltage-You MUST use a resistor or an incandescent lamp. Not doing this creates exactly the problem you have. Same with GM alternators, and Chrysler as well. Some regulators can handle this, but none were really designed to-so you get an unpredictable problem. Sometimes it works, sometimes it doesn't.


You're not helping things with the "no key" feature either-backfeeding the alternator is REALLY hard on the regulator.

Edited by Xnke
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I did the wiring for the regulator removal however it doenst matter anymore since I hotwired the alternator, Since jumpering the wires on the external regulator just sends constant and switched voltage to the alt.

Xnke, What size resistor should I use or what size light bulb whould be correct for the L wire?

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