Good alternator putting out low voltage


I learned decades ago to swap to a 140 amp-200 amp alternator,
as the stock 75-105 amp alternators on muscle cars and earlier corvettes are marginal at best/
if you shop carefully they can usually be found locally at some alternator re-builders for under $150
both my corvettes have 200 amp versions purchased NEW for under $250
while that may be over-kill to some I find the electric fans on the corvette and ignition and head lights work noticeably better

I have no problems putting in the higher amp alternator, but I am a bit ignorant when it comes to electronics on vehicles. And I don't want to put too much current through these 50 year old wires. And I would assume you are not setting me up for failure with this advice, I am just needing some knowledge on the subject.

I will get to the testing the warning light in a bit. As for the rebuilds I agree they are far worn out by now. This is my problem with Quadrajets nowadays they have been rebuilt too many times, when was the last one built, late 80s, that's alot of miles. But the QJet subject is for another time, and yes I am partial to them.


The Grumpy Grease Monkey mechanical engineer.
Staff member
puts no extra strain on the cars electrical system
IF its PROPERLY installed
with a 8 ga or larger cable between the alternator output and battery positive terminal,
(the only cable thats likely to see higher current flow)
IF your not getting the correct battery charge or the lights seem to brighten when the engine rpms increase, the first thing ID check is the battery cable connections and grounds to the frame and the alternator output at the alternator , then the ohms resisitance in major battery cable connections.
your issue may be the alternator or voltage regulator so obviously the components in the system need to be issolated and tested.
so the battery can easily take the higher current flow rate IF its ever operated where the battery capacity is being drained while the systems operating at full capacity.
simply because the components only DRAW current flow as required, to maintain the max designed capacity they would get with the old 70 amp-105 amp stock alternator , thus theres no higher flow rate , your not pushing the current the components draw what they require,
the difference is that when your running several components,
theres enough current produced to allow everything to still function at full designed capacity.
let me put it this way,
(I'll just make up amp values to illustrate)
if the old stock alternator is rated to put out,
lets say 90 amps

and your old head lights PULLED 20 AMPS
YOUR gauges pull 20 amps
your radio pulls 10 amps
your air conditioner fans pull 20 amps
your aux cooling electric cooling fans pull 20 amps
your electric fuel pump pulls 10 amps
etc, the old alternator is more than likely not putting out 80 amps
unless its spinning 3000 rpm
so if your getting 80% of the designed current to reach each component,
you would be doing good, if your cruising at 2000 rpm, at night,under that scenario, the head lights are likely dimmer than designed etc.
swap to the larger amp rated alternator and everything operates at designed capacity, and the alternator is never operating near full capacity so its under less strain.

Headlights (high beam)40
Headlights (low beam) 10-22
Tail Lights 8
Emergency brake light 4
Emergency flasher 15
Turn signals 10-15
Windshield wipers 6-20
Horn 15
Brake lights 15-20
Running lights 8
Winter starting 225-500
Summer starting 100-400
Approx. Avg. 300
Cigarette lighter 15-20
Interior lights 10-15
Instrument panel lights 4
Radio 10
Stereo Tape 10
Electric antenna 20
Air conditioner 10
Heater 20-30
Defroster 15-30
Electric seat 20
Electric windows 20-30

Typical Current Loads for Automotive Systems, Lighting and Accessories:
Engine Idling (no lights or accessories on) - 35 to 50 amps. This will vary depending on the number of cylinders (more cylinders draw more power for the fuel injectors and coils), the type of fuel injectors (some draw higher amp loads than others), the type of ignition system (single coil or multi-coil), the amp draw of the PCM, and the fuel pump (the amp draw will be higher with higher pressure systems).

Engine Off (nothing on) - 40 to 50 milliamps (power drain by modules in sleep mode, antitheft system and keyless entry)

Ignition Coil (single oil-filled coil older vehicle) - 3 to 4 amps.

Ignition Coil (single DIS coil newer vehicle) - 5 to 6 amps.

Ignition Coil (coil-on-plug) - 6 amps per coil.

Ignition System (primary circuit) - 6 to 20 amps.

Fuel Injectors - 4 to 6 amps peak, 1 amp hold

Electric Fuel Pump (depends on pressure and flow) - 4 to 12 amps

Electric Cooling Fan (depends on size) - 6 to 30 amps

Headlights (halogen low beam) - 8 to 9 amps per pair

Headlights (halogen high beam) - 9 to 10 amps per pair

Headlights (halogen high and low beams combined) - 17 to 19 amps

Headlights (High Energy Discharge) - 12 to 14 amps during initial start, 7 to 8 amps once bulbs are hot

Headlights (LED) - 0.6 to 1 amps per bulb

Small bulbs (incandescent) - 0.3 to 0.4 amps per bulb

Small bulbs (LED) - 0.04 to 0.06 amps per bulb

Starter Motor - 200 to 350 amps

500 Watt Sound System - 42 amps

Electric Rear Window Defroster - 10 to 20 amps

Windshield wipers - 2 to 10 amps depending on load

Heated Seats - 3 to 4 amps per seat

Power Windows - 3 amps

Electric Power Steering - 2 to 40 amps depending on load

Air Conditioner Compressor Clutch - 2.5 to 5 amps

Heater A/C blower motor (depends on load, size and speed setting) - 2 to 30 amps






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When you install a larger high amp alternator the Alternator case is Bigger in size.
You often have to get Creative with mounting brackets.
The Next series GM Alternator released after your 10 DN Is the 10si.
Its a Direct Bolt in .
6.00" inch end frame design both.
The 12 Si Has much higher Peak and idle current output.
End frame design is 6.250" inches or so.
Its a Metric design....used on 1980's big American GM cars.
I use a 12 si on my 1963 Grand Prix.
I rebuilt it myself about 12 years ago now. Still working.


The Modern Ford Alternators actually blow away any GM has other than Delcotron CS144.
Custom brackets made often required to use it.


I like Quadrajet carburators too.
Very limited supply of tuning parts today.
Ditto for Edelbrock AFB.

Holley 4-bbl best overall .
Use Vacuum secondary design for daily driving street use.
Lots of Jetting metering parts still made for them.


That is cool to see the original old literature.

I got my parts in and replaced the circuit board. Let the Camaro idle for a bit and tested the alternator warning light, nothing. Tested the volts coming out of the wire that attaches to the alternator warning light and it was getting 7.1 volts to it. If I understand correctly one of the wires at the pigail on the alternator goes to the dash alternator warning light. And I installed a new bulb to eliminate that being the issue. Should the pigtail be sending 12 volts?


No There is A Voltage Drop across the Tungsten Filament in the Generator Warning Light.
Actually Alternator but GM Refers as Generator in Factory Schematics.


The Warning light bulb is acting like A Resistor. Actually Varies Resistance and Current as the Filament Heats up or Cools Down.


Do You have at Least 12.6 Volts DC at the Battery with Your Camaro Running. ?


Here is another question I should probably already know, when does the alternator warning light actually come on?


The Alternator Light Comes on Ignition Key On Engine not running.
Goes off momentarily while cranking engine over to start in most Vehicles.

Alternator comes on if the engine dies out for some reason while driving .
Light comes on if there is a Charging system failure such as a Broken V-belt(s) Driving the Alternator.


12.6 volts is Ok Good.
If the Battery is Close tp Discharged state less than 40% capacity Reserve the Stock 10 DN Alternator is working hard.
100% Duty cycle.
Depending upon Diodes used in the Rectifier Bridge by.the Builder reliability will show....Last or burn up.
Best to charge your Camaro battery overnight.
The New Schumacher Digital Display Chargers are nice.
Wally World Walmart has Schumacher .
$99 or less .
Vintage portable chargers with Transformers had Copper...My Favorite .
Not made no more.
Just in Full Size Shop Battery chargers.

With a 100% Fully charged battery the 10DN alternator should read 13.5 -14.6 volts DC checked at the battery engine running & Camaro Headlights Switched Turned On.


10-4. Will Charge it and see what I am getting. I still have yet to get the warning light to come on. That is why I wanted to know when does it actually come on. Back to trouble shooting.



Went back through the information yall provided and I noticed I have no ground wire on my alternator and it never had one from the previous owner because I would have put it back. Maybe that will fix some of my problem. Back to the garage.


Well first let me apologize for not thoroughly looking through my service manual and wasting yalls time, although it was educational. There is NO alternator warning light on my car. What I am looking at is my fuel light. Besides my signal lights all I have is the brake light and fuel lights. Lesson learned.

Thank you for the help


Took the Camaro out for a short drive, and all is good. Alternator is charging 14.7-14.8. Can't put my finger on a specific cause for the low voltage output, but I did take out all the PO aftermarket radio stuff and fixed some of the wiring issues. Feels good to fix something instead of making it worse, now on to the next project, probably installing the new ammeter, old one has a broken dial/arm.

Thanks for all the help


The Grumpy Grease Monkey mechanical engineer.
Staff member
Even if your experienced in most areas of car repair, if you have questions ,its almost always a good idea, if you run into a problem, to post it, and to have several experienced members think over the issue and provided you with potential ideas and options you might not have thought of!
you might be amazed at the number of times I read threads and almost scream. did you check X. or Y. or Z?? and I'm sure that's the common response from most experienced mechanics

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