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1G Alternator? Battery? Other charging components?


Probationary Member
Aug 12, 2006
Salt Lake City, Utah
I'm having issues with the volts staying up at idle. They will chill right at 14.1-14.2 when I'm driving, and when i'm at a light, I can hear my heater die down and the guage cluster dim out and the volts will drop to 11.8-12.6 and I have a brand new alternator, and a red top optima battery. There is a weird wire hanging down coming off the set of wires that goes to the ground on the alternator, and I've never known where that goes. :confused: If you have any info please let me know. Thanks guys!:thumb:


Proven Member
Nov 26, 2002
Los Angeles, California
:tease: I had to learn this the hard way. :cry:

Luv 2 rally or Gtm (our board electrical experts :thumb: ) could give you a more definative answer about whats allowable for voltage drop, but I think anything more than a tenth or two of a volt drop (loaded) from the alternator to the battery will require further investigation.

As far as other cars ability to produce full current at idle, my wife likes to remind me that her car, (94 Nissan Altima, with over 275,000 miles), doesn't have any issues in that regard. :rolleyes:

It's just a "quirk" of dsm's, especially higher mileage cars.

All those connections from the alternator to the fuse to the battery, as well as the grounds, get a little bit loose/dirty/corroded. This gives just a little bit of resistance at every connection. When you add it all up, you begin to see funky symptoms, like random voltage drops, and lights dimming/heater motors slowing down.

Simply disconnecting the battery, and removing and cleaning the battery terminals, and each and every electrical connection to bare metal can make an absolutely magical improvement in situations like this, and is always a good place to start.

I've noticed that a slightly higher idle (~800 to ~850 rpm'ish) seems to help a bunch.

You can also use the 90 amp Galant vr4 alternator as replacement for your 75 amp dsm unit. Since I started using them, I haven't had any problems with low rpm voltage sag. :dsm:

Please, run a heatshield on your turbo/o2 housing/downpipe! The heatsoak from hot turbo/exhaust components at engine shutdown can really create issues with the wiring harnesses, alternator, and power steering pump. The exhaust system components are well over 1000*f, and that heat will just baste everything in the vicinity without the heat shields installed.

Sounds like your pop is pretty cool! You should be thankfull he is knowledgable, and willing to help. I learned more from my father and grandfather than I ever learned in school. :thumb:

Great set of posts, you should take your figures and put them in a Tech article for the board.

A previous poster mentioned 5,000-6,000 rpm, what he failed to include is that _is_ ALTERNATOR rpm and not Crankshaft (engine) rpm. To my knowledge only motorcycles rate their alternators at that high an engine rpm.

I have used a bit lower rpm of 1,500 but have seen higher numbers for different vehicles. If you really need to know just chalk mark the crank and alt pulleys. Then with a ratchet turn the crank by hand to count the alt revolutions for each crank turn. Using a target goal of 5,000 and 3:1 pulley ratio 1,666 rpm would work, if 6,000 then 2,000 crank should do the trick.

If memory serves there are some 100 and 120 amp alternators for 2Gs (automatic tranny?) though don't know if they will fit and there may be some wire issues.

It certainly can't hurt to run a second B+ from the Alt to the battery but since the factory had an 80amp or 100amp fuse you should include this in the second wire. Many of these will have provisions for bolt terminal connections but finding terminals to fit 8 gage wire will be diffult. Best bet for those is an auto stereo installer/supplier where they are used for the big 2,000 watt amplifiers. If you have a digital volt meter then probe the B+ at Alt and then at battery, should be the same. If not then start cleaning terminals, don't forget the 80-100 amp fuse as a source for voltage drop.

The capacitor mentioned is for radio noise suppression and will not affect charging voltage.

If you are really into DIY you can build your own carbon pile load tester from rather simple materials. Some of the ham raidio sites will have specs and list of materials.



Probationary Member
Aug 12, 2006
Salt Lake City, Utah
I ran 4 guage wire with an 80 amp fuse in it from the alternator to the positive terminal. Didn't help one bit just so you know. Cost about 20 bucks, so no big deal. I'll be rebuilding my alternator once I find someone local who will do it.:thumb:

Oh and I recommend getting a heat shield, wrap, or spray.. it's nice!:D


Proven Member
Mar 24, 2006
Never Summer Ra, Colorado
My alternator is good, and the one I changed out was good too, I had a hard time getting them to warranty that one.

My defroster is always on, button doesn't do anything when I push it. Go dsm!:beatentodeath:

I was thinking about the possible current draw here...

You've shuffled a few alternators through your engine compartment with the same results. Either you're getting a bunch of bad alternators, or there's something else going on.

You ran the tests, and the results show a functioning charging system, with only a problem at idle.

(I'm still waiting for the measured voltage, under load, at the back of the alternator, compared to the battery, but I think it's a moot point, given you've run an external wire to the battery from the alternator....(I'm more curious than anything else))

Anyway, I was thinking about it some more today, and if you're showing the indicator for the defroster all the time, that should be investigated. The rear window defroster grid is a huge current draw. (It's fused at 40 amps.)

If you add that on top of the hotel load (fuel pump, ignition, etc), that may be enough current draw to cause a substantial voltage sag at idle.

As`a quick test pull the defogger system fuse in the front fuse box. It's a green 40 amp big fuse, (refer to the box cover for location), and re test the charging system...

I'm hoping it's all good now, and you can start a new thread about how to fix the defroster switch, relay and/or the timer...

:)tease: go dsm indeed.:dsm: )

Talk about a self inflicted kiss of death, ROFL, your car probably heard you. :p


Probationary Member
Aug 12, 2006
Salt Lake City, Utah
I'm not anywhere near my car, but I'm going to go take a look at that as soon as I get home. As for the Alternators.. I bought an OEM one from a local place called Henstrom Generator, here in Salt Lake City. The guy there kicks ass and just took over the business from his dad and helped me out a ton. I ended up getting the OEM alternator for way cheaper than the AutoZone one.. PM me if you want their number, so you can get a hold of this AMAZING alternator. Didn't fix the problem, but it's a 95 amp replacement and it helped a ton. Makes about 13.1-13.7 volts under a FULL load. By the way, Toybreaker, all those alternators were not putting out enough voltage at Idle and I noticed the pulley on the AutoZone Alt was slightly bigger then the OEM one I have now, thus less rpms, and ultimately not charging enough. The guy at Henstrom ordered me an even smaller pulley than the one I have on the OEM alt to bring up the alt rpms up slightly and help charge. I'll get on starting that thread about the defroster button just as soon as I research it, and see if I can't fix it before hand. Thank you everyone, and to those who have the same issue, run a 4 guage, or even bigger wire to your battery, it helps a bunch. Thanks again. Good luck.:dsm:

Oh and, don't curse your car, it will get back at youOMG .... haha.
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