Q: Secondary air pump.

The air pump supplies the catalytic converter with extra oxygen so that it can efficiently catalyze any unburned fuel. On start up, the catalytic converter is cold and requires some help to quickly get up to temperature allowing it to catalyze unburned fuel more quickly. You don’t see a power drain because the idle is higher when the motor is cold allowing the alternator to supply plenty of electrical current to all the cars systems. I suspect you see the lights dim when the car is idling at a stop. During this time, the catalytic converter is least efficient and a little help from the secondary air pump may be necessary.

If there is a problem, you would have a check engine light on. If you do not, you are likely a person with good attention to detail and may be picking up on changes in the efficiency of multiple systems that occur in every car over time. The systems involved here are the alternator, catalytic converter and air pump. In addition, the idle could be lower than when it was a newer car. All of this is normal degradation of your vehicle and nothing to be worried about at this time. Unless of course there is a check engine light on or another failure you haven’t mentioned.

The air pump is an electric motor and electric motors require more electrical current to run as they age. This can result in the dimming of the lights. Catalytic converter efficiency degrades over time and will require more help from the secondary air pump, further requiring more help from the alternator. Alternators will suffer degradation as well in addition to a possible slightly lower idle speed which reduces the alternators ability to supply the car with sufficient current. The combination of all of these is the most common reason for what you are experiencing.

If you find you need further assistance, I recommend the following inspection. Electrical problems inspection

Good luck!