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Discussion Starter #1
in the 3 months i've had the car, on 2 seperate occasions the alternator would just stop charging and i'd barely make it home before the car totally died.
then, i'd let it sit over night, and it would work fine again.
well, last sat night, it did it, and when i got home i started poking around with the test meter. it was down to 8.5 volts, and the alt was doing nothing. ok, easy fix i thought. threw in a different alt, no dice. converted it to a 100 amp CS130 alt i had laying around- nothing. the wire that activates the voltage regulator was dead. checked all the wiring for continuity- all zero ohms, checked the bulb in the dash- and it was, of course, good. unplugged the harness at the firewall- no corrosion of free play there, either.
all grounds are good, tried 3 different batteries, all positive connections are clean and dry.
that was saturday night- on sunday, it worked great, and i drove it to work monday-15 miles away- only to have the car almost die pulling into the parking lot with a dead battery again. 12 hours later, when i got off work, it started right up and all the lights were bright and it ran great all the way home.
so what am i not seeing here? ignition switch? everything else on the car works good, but i am paranoid about driving it anywhere. i hate problems that don't allow me to fix them..
 

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A head scratcher for sure! On a 10SI & 12SI, as viewed from the rear, the left spade is for the bulb/voltmeter, the right spade is for the voltage sensing from a remote point.

This remote point comes from the ignition switch and has 12 volts on it with ign ON. Or you can tie the BAT terminal with the right spade.
 

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Discussion Starter #3
the big red wire on the plug is looped to the big terminal on the back of the alt from the factory- if it had not been, that would have been the first thing i tried. full battery power there.
something is causing the alternator to not get "powered up" from time to time...
on a side note, i had to wire the CS alternator different than the one in my Nova- i had to use a different wire in the plug to get it to work at all. on my Nova, i used the terminal that it shows in the tech reference section here- i think it was the second wire over from the big red wire on the plug. in the Buick, i had to use the one next to the big red wire to make it work. this is on the very same alternator that i took out of the Nova 2 weeks ago chasing a similar problem on that car- which turned out to be a bad connection that i made 5 years ago when i converted that to an internal regulated alt- so one would think the hookup would be the same.
truly weird indeed. i hate electrical gremlins.
 

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Hmmm..... I have a CS130 alt (OEM) on my dually and it has two wires plugged in/on it. One #8 red wire and a single wire on the plug for the voltmeter.

How much simpler can one get?

Unless there is a difference in conductivity from alternator case to neg battery post and/or BAT terminal the positive battery post, you got me.
 

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Discussion Starter #5
does anyone know how much voltage is supposed to come thru the little brown "idiot light" wire in the plg on the alternator? with the key on, it gets almost full battery power, but i thought there was supposed to be some resitance there or something like that?
 

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When no current is drawn/used/traveling, there will be full source voltage, battery voltage.

There should be some resistance, I think 35 ohms in parallel, its generally used for bleeding off voltage when turned off. Also, to provide a working alt in case the light bulb burns out.

I measured Buford's alt plug last night and between the neg battery post to each wire was battery voltage. However, potential difference across the pair was .04 volts DC. A definite difference. This is a 12SI alt.

With key on, alt off (not turning), 12 vdc goes to one side of the light. The alt being lower in potential, since its not working, bulb lights. As soon as alt fires up and starts changing/producing energy, alt supplies 12vdc to the other side of bulb, thus, light goes out.
 

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Discussion Starter #7
i figured it out- the harness that plugs into the back of the instrument cluster had a bad connection. kind of discovered it on accident when i was taking the dash apart to check the volt bulb again- set the cluster back in and started the car with my handy multimeter hooked up to the battery- 11.5 volts. got dismayed and ready to give up for the day to get other projects done, and started putting in the cluster screws while the car was idling- then the dome light got brighter all of a sudden and the meter read 14 volts. took the cluster back out and attacked the connections with a pencil erasers to clean the contacts and a little screwdriver to bend the pins up a bit for atighter fit.
since it worked, i went up to the Chev dealer and got a new plug for the alt, as i decided to leave the 100 amp CS alternator in there and the plug i was using was kind of crappy. that damn plug from GM was $26- but had leads a foot long and butt splice connectors with shrink tubing on them to put it in.
 
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