that's actually not accurate. The most stable power is right on the battery. The battery absorbs the waves, pulses of power and smooths them out.
This is why certain accessories must be wired to the battery. EFI computers, Vintage air controller computers as a couple examples.
The power right on the alternator stud varies greatly. this constant fluctuation of voltage is not good for your headlight bulbs.
If someone is selling a kit taking power off the alternator I simply wouldn't buy that kit.
If you look at the correct wiring of a 3 wire alternator. You will see that the small red, voltage sensing wire is connected back to the large red wire from the alternator stud. But well down line. At a junction block where a number of power wires are connected. This allows the sensing wire to sense voltage down stream and adjust the alternator output correctly. One wire alternators do not use a sense wire and only sense voltage at the alternator. I have run both. I can tell you there's a huge difference.
You say it's just one wire and it's the same on both ends. Disagree,
Just because it's one wire does not mean the power is the same on both ends. That's a very simplistic view.
GM Would not have run that small red wire on the alternator back through the harness if it made no difference on which end of the wire it was connected to. They could have run a wire 2 inches long straight to the large post. GM doesn't like wasting money. They ran that wire back through the harness to the Junction block to sense the voltage in the center of the harness. Because there is a difference.
Connecting the power for your headlight relays would be ideal right off the battery. That's the cleanest power source. But the end of the battery positive cable is much easier on our cars and good enough for headlights. Off the alternator really is a poor choice. About the dirtiest power on the whole car!

 

Our team would like the opportunity to learn more about the light flickering concern on your Corvette and investigate ways we can potentially assist. When you get the chance, please send us an email to socialmedia@gm.com. Be sure to include your Username and Forum name in the subject line, then provide additional details about your experience in the body of the email. We look forward to your contact.

 

Right, think of the power from the alternator as modified chopped ac power which is buffered by the battery as sort of a buffering capacitor, allowing a stable true dc waveform. Running things like radiator fans directly from the alternator post seems to be a good way to burn up alternators from what Ive read. Now if you have a 2wg wire going from the battery to the alternator post I would think it would actually be less of a concern but im honestly not sure. I power everything from the starter stud.

 

It would still be a concern. The alternator is the source of the Chop as you referred to it.
think of a still pond early in the morning. The water is like glass. You throw a big rock right in the middle.
This causes a series of waves right? Right at the impact point the waves are say 3 inches high, and they begin rolling towards the shore. The further they roll, the smaller they become. Electricity down a wire behaves in a similar fashion.
Now with your Alternator wire, it goes to a junction, then off to the battery, at that junction various other loads are being applied. Thus also smoothing the wave. The battery is like a big damper. It absorbs the power and levels it even more.
So, no matter the size of the pond or lake. Right where the rock hits the water and creates the disruption. The disruption will be the same at the impact point.
The alternator IS the impact point!
Running your headlights off of such dirty, disrupted power is a great way to blow bulbs regularly. They won't like such sweeps in power.

 

Lighting expert Daniel Stern also sells a relay upgrade harness. He mentions using either method....not one preferred over the other. He mentions that if your car has an ammeter it's preferable to use the alternator as the relay connection point. This thread is simply about an incandescent bulb.....not sensitive electronics.

 

Well Ken, believe it or not. But I have never heard of your lighting expert. And a quick google search didn't shed any light on him.
And your correct that we are talking about incandescent bulbs. Which by no means are as sensitive as a computer.
Which is why I stated that pulling power at the positive battery cable on the solenoid was sufficient.
Please do note how a incandescent bulb works.there is a fine wire that gets so hot it glows. Creating the light, as well as heat. It is under a vacuum which keeps that fine wire from burning out straight away.
Constant voltage surges can and do affect that filament in a incandescent bulb.
That's OK. You needn't believe me. This is a forum. We are here to kick ideas around. Nothing more.
I would pose this question however. Have you ever seen any automotive manufacturer pull power off the alternator to power anything at all?
Those electrical engineers that design wiring for automobiles certainly would have thought they could save many meters of wire if they just tapped off the alternator stud? Wouldn't they?
But none do.

 

They tap off of the starter solenoid. The only device in most C3s that is powered directly from the battery is the starter itself.

If the C3 had a battery mounted in the engine compartment, the wiring would look different.

If you pull more power than stock, be sure to upgrade the alternator cable, too.

 

In the case of most of the C3s, they actually do... The charge wire goes from the alt. to the positive starter stud which is directly connected to the battery. So connecting anything to that starter stud is the same thing as connecting to the alternator, maybe four feet of wire. You can disconnect the battery from a running engine/car and everything will still work, because ultimately everything is connected to and runs off the alternator when it is spinning fast enough. The battery's job is to provide adequate power when the engine is not running, such as starting, and it also keeps things going if the draw exceeds the alternator output, like a defective alternator or leaky diode...

I have seen lights dim on/off when an engine is idling so slow the alternator output is too low, especially if the battery is not 100%... Not sure what the OP's issue is, I know the lights draw a lot of current, the shaft on my switch gets warm to the touch after running the lights for awhile,, the relays are a good Idea, I may look into that..

Daniel Stern Lighting

60

 

Just saying- the thought for running to the alternator- is it's EASY. The manufacturer takes the position they don't wanna make it too hard for the customer to install-
BUT it lessens the effectiveness of adding the relays. So 'correct" has a caveat- just sayin. The original alternator output on these cars at idle can be as low as 20A- not fine to connect there...

The headlight wiring - alternator wiring was designed over 50 years ago- and was not designed to last more than 7 years nor handle anything "added-on."
The power to the headlights is soooo convoluted- running from the starter across the firewall in the cabin- to the ignition switch- branched off to the headlight switch-dimmer
then out to the engine compartment to the headlights.

It's sorta like spending a bunch of money on a high HP engine and using the stock fuel lines-

Here's an overview harness done right- fused AT the source of power-battery. Using this - the headlight/dimmer will see less than 1/8 A (.125A ) of current.
A really clean way to do it- less wires spliced by using a Bosch "Fog light" relay-
It has two switched output terminals rather than the common relay with one.NC and the other one NO
0 332 019 150
Summit Racing has them for $4- made in Portugal- and MUCH better than the Chinese junk out there

https://www.summitracing.com/parts/bch-0332019150?

here's the relay-



A relay holder- made by Bosch- won't melt like the Chinese cheap stuff-


I use a male connector- so you don't have to cut up the harness-



And for the connection- there's different types- cheap Chinese black one or the Delphi which handles the fiberoptics 68-71
2 wire- high beam Delphi 6288472 3 wire high beam Delphi 6288471

 

If only they made more efficient bolt in headlights that use less current than the very old stock filament bulbs (LED) all this redesigning of the headlight system wiring wouldnt really be necessary... And we would have the benefit of being able to see better at night as well.

 

LEDs everywhere else, yes. For 5 3/4" sealed beam replacements? Other folks use the road, too.

The relay solution also eliminates the convoluted path, eliminating voltage drops. What voltage do your headlights see through the stock circuit?

So, why not both?

 

Fair point but as you can clearly see the leds im running are dramatically brighter than the stock bulbs with stock wiring. Ive never tested the voltage at the bulb harness honestly but most of the issues here being discussed are caused by halogens pulling higher current (more amps) through the weaker wiring not optimized for it.
If you eliminate the need for higher current in the first place its a win win for the electrical system battery and alternator included vs just beefing up the wiring to allow the halogens to more easily pull more power from them.

Someone made a reference to installing a high hp build and using the stock lines... Well what if you could have the high HP while consuming a lot less fuel? would you still replace the stock lines? Why not eliminate the issue vs redesigning the wiring for old inefficient lighting tech? Especially if its the simpler solution to implement? I dont think they even make vehicles with Halogen lights anymore let alone sealed beams.

And as far as the replacement for sealed beams blinding people that is because of people using aftermarket sealed beam type housing meant for halogens with a different reflector pattern than the correct design for LED which would have to include a focused beam with proper cutoff to not blind oncoming traffic. This is why I chose the lights I chose. they have a nice cutoff to avoid blinding others. its also why I use the correct projector style aftermarket housing in my truck with the HID bulbs as well. the pic below is my C3 lights

 

Funny, my search found it. I suggest you stop using google.

Daniel Stern Lighting

Here is his writeup on relays and wiring:
Relays

I agree with him, if you have spikes coming from your alternator, however small, you have a problem. The voltage regulator job is to convert the AC to STEADY STATE DC. I guess we'll just have to agree to disagree. I did do 4 years of electrical engineering school but what do I know.

 

I will point out just for reference a few years ago as im no expert myself on it. I had originally planned to wire my electric fans from my alt post after installing a higher amp alt and beefing up the wire from alt to the starter and I was told how it was a non no to do so and how it would damage my alternator. Some comments were..
Also I build a dc power supply with a bridge rectifier to drive a 90v dc motor once and the website where I got the plans suggested using capacitors to smooth out the crude waveform so I do believe the output of an alternator to not be ideal in its raw form. and I would think turning the lights on would still provide a spike in transient load on the alternator mentioned above or no?