Lights fluctuate/dim down at idle...

[shamanie]

When at idle, the lights will dim kind of. It goes with the slight shudder of the engine. Unfortunately, I can't really find the words to describe it any better than that. It really hadn't bothered me until I installed some new 3.5" dash speakers and they began to pop or distort (when turned up loud, not real, loud but you know) when that shudder happens.

[NH2112]

Sounds like a ground problem to me, check for missing ground straps or bad connections, and maybe make sure you don't have any shorts to the body in your new speaker wiring.

[HowieE]

The first thing I would check is the alternator output at idle. Test with a voltmeter at the battery while engine off, at idle, and then about 1000 rpm. Each should show an increase

[dieselbegreat]

I've had a couple alternators with shorted diodes inside that give low output, get very hot when running, make whining noises, etc. Also had a couple with loose internal regulators and loose BATT terminal that would flicker the lights, cycle on and off, overcharge the battery (one literally blew the caps off on a hot summer day sitting in traffic).