jersey280 Posted August 30, 2022 Share Posted August 30, 2022 (edited) Hey guys, Recently completed the internally regulated alternator swap on my 76 280z. I utilized a brand-new alternator from a 1983 280zx NA. I followed the directions from atlanticz, specifically the part for the 1976. The issue I am having is the alternator will not start charging the battery until I rev the engine over 3.5k. Once I do, it maintains a constant 13.8+ and works perfectly. I began testing and noticed the bottom plug to the "T connector" has zero reading at all times, including in the ON position when it should have 12v. I believe this is called the "L" connection. From what I believe I have gathered from searching, this is some-how tied to charging lamp, but also the excite for the alternator to start charging? If so, I have removed all stock gauges and went with speedhut gauges. Is it possible that the lack of a charging light is causing a break in the connection and causing this issue? if so, any suggestions how to work around this? Thanks so much! p.s..The new gauges also eliminate the parking break indicator, so I just cut the yellow wire under the passenger seat to solve the battery drain issue that is specific to the 76. Edited August 30, 2022 by jersey280 Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 30, 2022 Share Posted August 30, 2022 2 hours ago, jersey280 said: . Is it possible that the lack of a charging light is causing a break in the connection and causing this issue? Yes. You'll need to supply switched power to that terminal on the alternator. Quote Link to comment Share on other sites More sharing options...
jersey280 Posted August 30, 2022 Author Share Posted August 30, 2022 Thanks NewZed! It's easy to find a 12v source that comes on with key in the ON. Unfortunately, I cant seem to find one that gets 12v at ON, but turns off after car starts. Any suggestions? Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 30, 2022 Share Posted August 30, 2022 It doesn't need to turn off after the engine is running. But you might need to install a diode in the circuit. When the alternator is charging the current flows the other way. That's why the Charge light goes out. It can keep the engine running after you turn the key off because it's feeding the system through the wire. Look up the 240Z alternator swaps to see what I mean. Check the wires in the external regulator plug to see if one of them is switched power. I seem to remember that one of them was, besides the L wire. I had a 76 too. Here are a couple of links showing the diode. If you find a switched power wire at the old plug area you could probably just wire it up there. Or try it without a diode and see what happens. You can always drop the clutch while in gear to kill the engine if it stays running. https://woodworkerb.com/home/datsun-240z-rebuild/datsun-240z-alternator-upgrade/ https://www.classiczcars.com/forums/topic/46888-240z-alternator-upgrade-instructions-w-pictures/ Quote Link to comment Share on other sites More sharing options...
jersey280 Posted August 30, 2022 Author Share Posted August 30, 2022 I'm diagnosing her now. I think I found a green in the old plug that is switched power and I'll see if she wont turn off. Quote Link to comment Share on other sites More sharing options...
jersey280 Posted August 30, 2022 Author Share Posted August 30, 2022 Alright, Green on the plug was a no go. I did however temporarily rig it to a switched to a switched green I had inside the cabin. 14v immediately on start and she turned off as soon as I turned the key off..Problem solved, thanks again! Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 30, 2022 Share Posted August 30, 2022 I am not 100% sure that you shouldn't have some resistance on that circuit. You might want to search around bit to be sure. Normally the Lamp offers resistance in to the alternator, and blocks the current coming back. It would be a bummer to overheat the circuit in the alternator and possibly damage it. You could put a resistor in line or even a light to be safe. Or, even better, a fuse. Or both. 10 amp would probably be about right. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 30, 2022 Share Posted August 30, 2022 (edited) Here's a link. I'd add a resistor. It's the heat that kills them so you probably haven't done any damage. https://www.onallcylinders.com/2018/04/27/ask-away-jeff-smith-keep-killing-alternators/ " On most late model alternators, if the warning light circuit is not employed, running without that resistance in the circuit will cause the alternator to fail. On the plug-in connector, there are four connections labeled P-L-I/F-S. The connector labeled “L” is the only terminal (of these four) you will need to connect to the vehicle. If you choose to not connect a warning light in line (in series) with the wire terminated at switched (12v) power, then you must include a resistor. Our friends at Powermaster recommend an 82 ohm, 5-watt resistor. You can find these at an electronics store or online through a company called Mouser Electronics for less than $1." Edited August 30, 2022 by NewZed Quote Link to comment Share on other sites More sharing options...
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