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Thread: alternator output, whats too high?

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    Registered User 2sixTZombii's Avatar
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    Default alternator output, whats too high?

    I installed a 280zx alt in my 260z, I had it wired up perfect but the "sense" wire had no power going to it, I ran a jumper wire to the battery and I had 14.6-14.8 output. Awesome it works, but I've just been connecting and disconnecting the jumper wire when I go to start it. I heard on most alternators you can run a constant power wire for the sense post but, the factory had it get power there when the key is forward. As I read its through the wire that is supposed to supply sense power that the gauge is run. I don't that much about the gauge right now. I tried running it off of a "run" position power source, but as some power is lost through the switch I now read 15.08. That will work until it's fixed properly,if it's not too high output. Can I run a constant power wire to the sense side of the plug, or will it cause a drain? And is 15.08 too much? Those my main two questions.

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    Registered User beermanpete's Avatar
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    15.08 is within spec on the ealrier models, to about '76. If you are using a lead-acid battery it is fine. Some of the newer battery designs don't like that much voltage. The original design of the car senses the system voltage in the main wiring harness under the dash, not at the battery. Any voltage difference between those two points is due to wiring resistance (unavoidable). As the cars age this resistacne increases and the battery voltage will rise with it. If you pull the sense signal from the battery then the system voltage will be low by the same difference (15.08 - 14.8 = 0.28 in your case) so the system voltage will be 14.52. Not really a problem in most cases.

    To sense voltage at the battery without creating key-off drain use a relay that is controlled by the ignition switch.

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    Registered User 2sixTZombii's Avatar
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    Am I too understand that the sense wire originally leads from the alternator N side of the plug through a yellow wire to the regulator back out the regulator through a white/red wire to the anmeter out the other side of the anmeter to a 12 volt ignition source at the fuse box, as explained at this page Nissan/Datsun Z Car Voltage Regulator Conversion now he says "charge lamp" not anmeter which may mean I'm misunderstanding how it works. Now after the conversion for the internally regulated alternator once you jump (at the regulator plug) jump the white/red wire to the yellow then the S side of the new alternators plug should lead through the yellow wire to the anmeter (or charge lamp if I am misunderstanding) to the 12 volt ignition source at the fuse box, where the new alt gets its sense. Now keep in mind I have an early 260z so my wiring is colored different than most z cars.
    Alot to follow I know.

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    Registered User beermanpete's Avatar
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    In the original set-up (260Z) the N terminal (yellow wire) goes from the alternator to the external regulator. The N terminal also connects to the stater interlock system. The F terminal (white/black wire) also goes from the alternator to the regulator. The IG terminal (white/blue wire) comes from the ignition to the regulator to turn the charging system on and off and provides the voltage signal. The L terminal (white/red) wire is for a charging lamp (idiot light) and connects to +12 through the ignition. The L terminal also connects to the starter interlock system.

    To make the ZX alternator work in the 260Z you need connect the S terminal directly to a constant +12 line and connect the L terminal through a charging lamp to an ignition controlled +12 line.

    The external regulator can be removed. If the starter interlock system is still operating as originally intended the car might not crank and you will need to modify the wiring for it accordingly.

  5. #5
    No more body roll! SteveJ's Avatar
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    The yellow wire is also the power for one of the coils for the electric fuel pump. Leaving that relay in will cause a battery drain if you go to an internally regulated alternator.
    73 240Z
    74 260Z

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