Here goes.
I replaced original alternator in May 2014. Dash light on and the volt meter down.
Later in fall noticed interior light (oveer-head spotlight) pulsing or flickering.
In January of 2015 the headlights started to flicker when slowing down to appx. 1000 rpm and down.
I cleaned the ground wire(s) that I could find in the engine compartment. Cleaned the frame wire twice.
I cheated 5 years ago and I altered the headlight switch so the fog lights were on whenever I turned any lights on.
The garage I took it to (to diagnose the flicker) found my alteration and a blown fog light fuse.
They checked voltage output with all items running on high. Voltage spec'd out 14.0 I believe.
I called the alternator rebuilder and he asked me to check the connector for loose wires and such-nothing found.
He replaced alternator under warranty. Still flickering.
I found a thread here that suggested the tensioner (mine was original) be replaced, I then replaced the belt, tensioner, and idler.
Still flicker.
I am next checking the interior grounds?
Any idea where and how many?
Any other thoughts?
Headlight switch maybe?

 

I might've missed it on the post, but what condition is the battery in?

 

I have to confirm-but I believe 2 years old.
Started it up at -20 on Lake of the Woods on 12/29/14.
Will post it.

 

I can't get to much out of your post except you have some issue.
Start from the beginning and check out the system.
1. Is the charge lamp on at idle?
2. Does the system charge at all?
3. What is the voltage as measured with a voltmeter at the battery just after starting. Dis regard the dash meter for the present.
4. What is the voltage 5 minutes after starting and running?
5. Is cranking slow?

The answers will tell me what your issue likely is.
Good luck.

 

The answers to the questions:
1. No charge lamp on at all. Replaced alternator because the lamp came on in May 2014.
2. This is my daily driver, so yes the system charges. Has been with no issues even at -20 degrees in northern Minnesota. (post 2).
3. After starting the voltage is 15.16 volts.
4. The voltage after 5 minutes of running does rapidly fluctuate between 13.7 and 15.2 volts.
5. No it does not crank slow unless it is -20 degrees then it is expected.
Now that I see the rapid voltage changes I am bringing the battery in for a check.
It was purchased 10/11, so there could be an issue.
Will post results.

 

Ok, your report tells me the alternator regulator is the cause of the voltage flutter.
It may be the regulator or the plugup on the alternator.
The regulator is the only output control in the system uses unless there is an intermittent or fault to cause the reaction.
Your battery is being charged in the normal way, just the voltage is fluctuating because the alternator field is being controlled in a faulty way.
Find the cause and the system will be normal acting.
Good luck.

 

When I installed the second alternator (that was covered under warranty) I checked the plugs into the unit.
Nothing was loose or corroded.
I am taking the battery in tonight for a check.

 

This is just a comment based on what you reported.
I would say the battery is in good condition if it cranks the motor under cold conditions.
Only thing that could be an issue is the age and capacity for 'cranking time' or reserve power.
Good luck.

 

Mills Fleet Farm kept battery overnight, the testing equipment asked for a complete charge and retest last night when I brought it in.
It failed, I have a new battery and flickering lights.
I am going to get the connectors that plug into the alternator next.

 

Replaced both connectors on the alternator to no avail.
Checked ground under drivers side kick panel, found it corrided.
Still flickering, here is what happens:
I rev motor up to 2-3000 for 5-10 seconds with headlights on neighbors garage.
Heater blower on low or high speed, interior spotlight on, I let off gas and when tach hits 1000 the lights dim.
One note, the voltage when checked with meter at the battery when running is at 15 volts-that sounds high.
I will be calling the alternator rebuilder next.

 

Called re-builder, the colder the ambient temp the higher the voltage.
He tells the same thing-ground issue.
May have to go to dealer.

 

Sounds like a bad ground somewhere. Also test for alternator amperage. An alternator can put out volts and low amperage. 15 volts means squat if it's putting out 20 amps. The alternator should be putting out close to 80 amps plus when its cold as hell and lights and heater blowing full bore. A.W. sperry makes a meter that will read higher amps for both AC and DC. It is possible the Alt. builder got some bunk regulators. A bad ground could also cause a fluctuating voltage and show spikes in amperage as well. High voltage could be due to resistance IE bad ground trying to push the amp draw needed.