Car sat for ~3 weeks. I go to start it and it starts, but weakly. I drive it to work. Come home, no problem.

5 days later, its deader than dead, not even a solenoid click. Put it on a 2A charger overnight. Battery goes to 12.62V. Starts up perfectly. $250 battery is less than a year old.

Check voltage on alternator and its 14.5V at the alternator posts when running. Check voltage at battery with the car running, 12.6V and falling very slowly. When things have been working normally, the battery measures the same voltage as the alternator when running Gauge at 0. Usually it runs slight positive but is sometimes erratic jumping to +20 or 30. I've found and cleaned and greased every ground in the AIM. Headlights dim at idle, but brighten at 1200rpm.

I've replaced the regulator at least 3 times over the years (taking stabs at the problem), the last one being the $70 AC Delco. The alternator was marked "not internally regulated" and replaced less than a year ago.

That's all the clues I have right now. Thanks.

 

Take a voltage reading at the starter terminal where the battery connector hooks up. BE CAREFUL not to short anything out and to not burn yourself.

If the voltage at that point is also 12.6v, then you have an open on the lead coming from the generator output. If such is the case, then I would suspect an open fusible link.

If the voltage at that point is 14+, then you probably have a bad battery lead connection either at starter(doubtful) or at the battery (more likely).
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Here is where the fusible links were located on my 68 when I inspected and repaired them to get my ammeter working:

https://www.corvetteforum.com/forums...locations.html

I would also recommend getting rid of that old 10si & external regulator, and rewiring then installing something like a CS-144....mine is just fantastic.

 

Thanks. I'll try that this weekend. I need to look at the wiring diagram to (hopefully) understand that. I don't suspect bad battery leads. They are relatively new and corrosion free...both ends polished recently. I guess I thought if one of those FLs was open it wouldn't run but I have not run any continuity testing.

 

Read this. Could be something very simple. For me it was a bad switch in the rear center console.

Mark

http://www.popularmechanics.com/cars...attery-drains/

 

You could have other issues, but the suggestions I made were based on the statement that you only read 12.6 volts at the battery while the car is running.

The swinging ammeter could be something making intermittent contact and causing intermittent charging. I had that same issue before and I cleaned up and rewired the wires at the starter area. This was a separate issue from my fusible link issue.

You could also gently wiggle the leads at the starter area, horn relay area, and at the bundle near the wiper motor to see if the battery voltage goes up (running of course) this might give you an idea of where the potential open might be.....carefully again you don't want things sparking and shorting.

 

I've done this already 14 mA draw...the clock.

Good thoughts. I think intermittent is the key word.

Any thoughts on headlight dimming on idle?

It appears that battery charging goes through the horn relay with a fusible link. There is a Black/white wire to the ammeter with a fusible link. I don't understand where this brown wire goes from the #4 leg of the regulator.

Also can you point me to any good "how-to's" for the internally regulated alternator. Electric fans are on my short list so I'll need to switch anyway.

 

Look at the 2 wires on the plug that goes into the side of the alternator. Mine were corroded and a new pigtail solved my ongoing problem.

 

Until you resolve the basic charging issue. It may be a non-problem after that.

Let me go look for some old forum posts from when I installed my CS-144.

My external regulator has been removed and system rewired so I can't help you with that.

Back in a little bit.
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[QUOTE=Kevin68;1588955146]I've done this already 14 mA draw...the clock.



Good thoughts. I think intermittent is the key word.

Any thoughts on headlight dimming on idle?

It appears that battery charging goes through the horn relay with a fusible link. There is a Black/white wire to the ammeter with a fusible link. I don't understand where this brown wire goes from the #4 leg of the regulator.

Also can you point me to any good "how-to's" for the internally regulated alternator. Electric fans are on my short list so I'll need to switch anyway.

 

follow this thread.... this is for a CS-144. (For my 68 I went to NAPA and bought a 12si-to-CS144 pigtail adapter (Part number Echlin EC82).
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Try using this to figure out your adapter. Follow the guidance as written. Worked the first time for me. Go to your local parts store and get the equivalent pigtail part number:

The site below tells you how to figure out which adapter to buy for your CS-144 tie in to your 12SI: I also added the key paragraph below in case you cannot open it.

LINK REMOVED...IT DOESN'T WORK ANYMORE.....follow guidance below:

"If you are unsure which adapter to use, measure the resistance of the exciter line. Disconnect the positive battery cable and the alternator plug. Connect an ohm meter between the #1 terminal on the plug end of the alternator harness and the end of the positive battery cable. Turn the ignition key to the "on" position and read the ohmmeter. If resistance is less than 35 ohms, use adapter #8078. If it’s between 35-350 ohms, use #8077. If it’s more than 350 ohms, you have excessive resistance somewhere in that circuit which needs to be repaired, first."

take note of how to measure the resistance in the circuit so you can figure out which adapter to make or just buy.

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Here is a website to bypass the external regulator to and convert to internally regulated for a 12si ....it's for pontiacs, but it's generic for gm external regulators...you can search for another if you are uncomfortable.


http://www.wallaceracing.com/alt-conversion.html

And here is some more info (Buicks methinks

http://www.rowand.net/Shop/Tech/Exte...Alternator.htm
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follow the wiring to convert to a 12SI alternator and then you can get the above mentioned adapter to connect a 12si wiring harness to a CS alternator. The reason I say this is because I did it...and if I get in a bind I can always get a 12si alternator and plug it into the vehicle harness by taking out the jumper.....not really a concern now that cs-144 alternators are so common.

You can find the adapter from 12si wiring to CS-144 by using your favorite search engine and looking for something like:

"alternator conversion wiring harness adapter"

 

Thanks Carriljc and others with suggestions (My 76, pigtail connections were clean),

Found the problem, the screws holding the #10 red wires on the horn relay were loose. Tightened them down. Started it up. Voltage difference between alternator/horn relay voltage and the battery is 0.12. I'm assuming this is line resistance. Gauge is working normally too.

I didn't do exactly what you said but I get the idea of what you were suggesting. I started up top simply because it is easier to get to. My headers effectively block access to the starter from the top. Going out for a test drive...jumper cables and meter on board.

Thanks again.

Back from test drive. Gauge operated perfectly. Just slightly above 0. No erratic-ness. Moved slightly more positive when I turned on the headlights.
The headlights still dim a little at idle but not as bad. Bonus fix was the jumpiness I had in the electric tach (when I activated brake lights or directional signal) that I attributed to a lack of a filter. I think I'll use the time saved on this to go around and check electrical connections I can get to.

 

"while you're at it"..... well, if you still have that 10si with an external regulator it can probably barely keep up. Put a voltmeter on your battery terminals (with engine running) and check voltage....then turn on your high beam headlamps....I suspect (if it's like mine was) that the voltage drops significantly. After that then turn on all your loads (fans, a/c if you have it, stereo, brake-lights, flashers, and see what your voltage is. I used to have the 63 amp(or was it 65 amp?) 10si and it could barely maintain voltage above the voltage that the battery had w/o anything running.

Anyway, once you get tired of that alternator I recommend a CS-144.

Have fun and good work