I replaced my alternator & battery some months ago, and all was working fine until recently...
The battery dash light started to flicker. Sometimes it will go completely out, or be fully lit, but it is just a matter of seconds before it goes back to flickering.
For some time I have noticed my clock illumination wandering from dim to bright. I suspect a loose connection since a sharp rap on the dash brings it back. Maybe this same loose connection(ground?) is causing the flicker.

I have checked the battery:
Both battery terminals clean & tight.
Electrolyte topped up.
Hydrometer says all cells OK.
Starts right up with no dimming of lights. (I did replace the starter but I think this was unrelated).
Used a known good battery to replace mine - no difference.
The battery is not the problem.

I have checked the alternator:
Bracket & belt are tight. Wire connections are clean & tight. Moving these wires around slowly made no difference with the flicker.
Produces 14v - in spec.
Disconnected positive terminal from the battery to check raw alternator waveform with oscope. Looks good - no evidence of bad diodes.
Autozone alternator tester says it is fine, but does it test the L terminal?

I have checked these connections:
Positive connections on starter, alternator, and under hood fuse box.
Ground connections on body near battery, on block below oil filter, on intake plenum.

The fuse box & fuses check out OK.
Pulled the ignition switch and it checks out OK.
Disconnecting just the white alternator wire at the battery positive terminal causes the charge light to go off as it should.
Disconnected just the alternator 3 wire plug. With Key off, Engine off, the plug contacts measure (1-L,2-IG,3-S) 0v,0v,12.5v. This looks OK.
With Key on, Engine off, the plug contacts measure aprox (1-L,2-IG,3-S) 11.8v,12.3v,12.5v. This also looks OK. The lamp circuit has a bulb and diode drop as expected.
Pulled the instrument cluster. There are 4 diodes soldered to the flex circuit. The diode tester in my DMM say they are good. Checked continuity from battery lamp to L terminal. All OK, no shorts.
The current draw from the battery with just the engine running but 3 wire alt plug removed, is about 12A. Not sure what to expect. Try again with B+ wire disconnected to see the diff.
I don't have DRL, and the section of wire from the lamp/diode to the alternator L terminal checks out OK. Battery charge light goes on only when this wire is grounded.

Other suspicions:
Power & ground for the entire dash? Explore this while doing ignition switch.
Some other bad connection hiding in a cable or crimp? First look for intermittent short to ground such as the backup light cable issue.
Faulty alternator not controlling battery light correctly (terminal L)? Look at three terminal plug and voltage drop for each wire.

 

The place I bought the alternator offered to bench test it. I really didn't think that was the issue but it was only 15min to remove, and digging into the wire loom could take hours. The alternator was faulty enough that the test machine would not even spin it up. Another 20min and I had a free replacement installed and NO FLICKERING CHARGE LIGHT.

UPDATE: Some time after the repair, I purchased a clamp-on DC current meter and measured the current draw by clamping on the ground cables from the battery. With the key turned to ACC but no accessories on (no dome lights, radio, no open doors), the total draw is about 1A max. With the key turned to ON, this is about 5A max. These readings may be useful for future diagnostics.

Measuring current after the car is started is less useful since the alternator will initially charge the battery at 10A or more, but this will drop quickly and hop around as the battery is topped off and the voltage regulator does its job.

 

Thanks for posting what the problem was and what fixed it!

 

So I am having the same issue but the Battery light is on all the time.

I have Weak power windows & Windshield wipers but it appears to have good start power however i replaced the battery thinking this would solve the problem.

Tested the alt on the bench / I believe it was below 14 but real close to

anyone have. Any ideas ?

 

You can see all the diagnostics I went thru only to find it was the alternator after all. Apparently they can behave just fine except for the circuit driving the L terminal/battery light. Does the light go out when you disconnect the white wire from the battery? Does anything change when you wiggle the 3 wire plug and wiring?

The circuit driving that light is a single wire running from the instrument cluster thru the ignition switch to the L terminal on the alternator. If that wire is grounded anywhere along its run, it will complete the circuit and the light will go on. On canadian models there is also a daytime running light circuit off the same wire at junction J5 under the dash, but you probably don't have this. If you disconnected just the L terminal wire (shown as yellow with green stripe on the diagram), that would tell you if its the alternator or not. I don't remember if it is possible to disconnect just that wire without cutting it.