Q: When my car starts I see my headlights and indash lights go dim.

asked by on February 06, 2017

I also notice that when I turn my key to "on" my sub in my car makes a bump every few seconds even without using my stereo.

My car has 88000 miles.
My car has an automatic transmission.

A starter motor uses a lot of current and thus will cause a voltage drop at the battery. During the brief interval that a starter engages and runs, any other circuits that are also "on" could see the voltage drop and, in the case of lighting circuits, bulbs will dim. The dimming will be more pronounced if the car battery is old and/or the car wiring has poor ground connections, and high resistances, much of which come with age. You should have the battery tested in a load test. Batteries are very important. If the battery only has a marginal pass on the load test you should just simply install a new battery to reduce diagnostic headaches. Charging system output should also be verified against factory specifications To have the alternator inspected please request an alternator inspection/replacement and the responding certified mechanic from YourMechanic will get this resolved for you. As far as the sub, the problem you are describing may mean the system is powered when it is not supposed to be. That would have to be investigated in an electrical diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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