2002 Avalon lights flickering...

No, but it might be the voltage regulator built into the $100 (for a full rebuild at a good local shop) alternator. Or the carbon brushes on the alternator rotor field slip rings could be worn and on the way out, but a rhythmic blink like that would be odd for brushes.

Or there's a 'blinking' load on the system like the gauge voltage regulator in the instrument cluster, and there's a loose connection from the battery somewhere causing a voltage drop, making the pulsing load much more apparent. My first impulse would be to check all the battery cable connections (both positive and negative) and the chassis ground straps really carefully.

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Thanks Bruce... After your answer, I doubt if it's the brushes, because the rhythm doesn't change with engine rpm. I've admittedly not messed with the negative connection, so I'll try that before taking it to a shop.

I'm having problems with the positive post connection because there's a plastic "shield" thing that sits below the clamp (and next to the battery) and that also has a little plastic spacer attached to it that goes up vertically between the two halves of the post clamp. Because of that spacer, I can tighten all I want on the post bolt, and it won't clamp the battery post tight enough to prevent my moving the connection on the (cleaned) post with just my hand and a big grunt. (Does that make sense?) I wouldn't think I should be able to move it at all if it's tight enough. BUT, the blinking does go away when the engine is stopped.

-- Steve