Hello, I was wondering if anyone else has experienced this problem.
When I"m idling, I can see the battery light dimly lit... this goes away If I tap the gas pedal or turn on the headlights... does this mean my alternator is going bad?
By the way, it has been doing this for a long time (said the previous owner). Anyone have any suggestions?

 

It sounds like the alternator...

I'd assume the reason it's dim when the car is on is ur not getting sufficient power to the electrical system, and the reason it is not on when the headlights are is because the headlights draw so much there isn't enough to amperes to light the dummy light (battery light).

First check the battery, see what that's putting out, only thing I can say is swap batteries, see if it charges one while running, if it doesn't, then it's your alternator, I'm not positive on how to test for alternator workings, sorry.

 

the battery light should really be changed to a picture of an alternator cause that is 99% of the time all it is, yes your battery might be bad due to it not charging sufficiently and draining the battery fully will wear it down a LOT faster.

when the car idles it isnt using the charging system as much and it uses the low diodes, when your lights or a/c are on or your driving, your alternator is producing more in the higher output range using the high diodes hence the light going off due to the alternator producing a sufficient output

in other words, sounds like your low diodes are shot but your highs are still good so basically replace your alternator and have your battery fully charged and tested to see if the bad alternator damaged the battery with time