alternator help on my L20b please

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alternator help on my L20b please

Post by tay » 20 Apr 2009 15:06

Hi, I believe my alternator went out today, going to confirm with a multimeter this afternoon.... I want to be sure that it is not the voltage regulator, so would I hook the multimeter to directly to the alternator lead? Is there a way to test the regulator? Someone at kragen tested the battery and it was 12.2-12.3 or lower with the head lights, and he refused to put it on the alternator for me so I don't know which of two is bad, alt, or regulator.

I'm thinking about putting a alternator from a 81-88 720, but it is internally regulated; does this mean I would have to get rid of the voltage regulator and re-wire a few things? Should I stick to an external regulated one from an older 70's 620?

Or perhaps someone can suggest a decent alternator with 60+ amps for my L20b.


edit: I'm also torn between painting my car black, mustard yellow, pickle green, orange, or pistachio green. Any suggestions?

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Re: alternator help on my L20b please

Post by defdes » 20 Apr 2009 16:11

Stock colors? If so, Pistachio, Orange and Mouseturd are my favorites.

As for your alternator, go for the 60Amp IR, clean up the engine bay a bit. It requires a bit of splicing but very easy.

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Re: alternator help on my L20b please

Post by datzenmike » 20 Apr 2009 17:13

All alternators after '78 were IR (internally regulated) The L20Bs were usually 35 or 38amp output. The 720 were 50 and 60. (Canadian ones were all 60, never seen a 50 amp) However they are larger diameter than the L20B 38amp. Should fit a 510. I have been told that an 8'88 and up VG30E (not DE) Maxima alternator will swap in if you swap your pulley onto it and drill out the threads so the stock through bolts will work. This alternator is smaller than the 720 and is designated LR 19 making it a 90amp output. Nothing wrong with nice bright headlights, tornado defrost and hammering wipers while idling at a stop light. Rebuilt ones are around $150 and up but there should be lots in the wreckers by now. Clip the wiring and plug and take it too. And as I always say, I would rather have a good used original Nissan part than a re-manufactured one.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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Re: alternator help on my L20b please

Post by banzai510(hainz) » 21 Apr 2009 09:46 ... ss=&sort=1

Just make some Jumpers and use the color code of the wires where the volt reg used to plug in.

the photo shows 1jumper but youll make 2 Jumpers using the colorcodes mentioned in above drawing.
Or go to the Dimequarterly website FAQ section

also most Volt regs when they go bad will overvolt.higher than 14volts. That means the alternator is good.

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