Headlights/TailLights/MarkerLights

[57rookie]

So, I dont ever drive my truck in the dark so I never noticed before but I started it up in the garage in the dark to show my daughter my new Thrush Rattler exhaust I installed today and I turned on the lights.
I noticed right away that my marker lights, headlights, tail lights, and dash gauge lights were going from bright to slightly dim and bright again , basically flickering.
What would be the cause of this???????
Thinking alternator but my battery is solid and the alternator keeps it charged very well and it sits for weeks between start ups.
Thoughts????

[clay68c10]

It could be the alternator starting to go out. They can get erratic and still charge, just not at a steady even voltage.
It could also be a bad ground.

[VetteVet]

Turn on the lights without starting the engine or turning on the key. If the lights are solid but dim then start the engine and let it idle and you will probably notice the dim and bright situation. If so then hold the accelerator at a higher rpm and notice if the lights get bright and steady. If they do then you have the classic symptoms of the OEM alternator and external regulator which is, low output at idle. The best fix is to convert to an internally regulated alternator with higher amperage. Simple to do and if you intend to upgrade the electrics you will have to do it sooner or later.