notice this when I drive at night with healights on..

whenever I brake which causes the taillights to go off, use the A/C fan, even the turn signals, my headlights dim very noticably. It's like anything electrical that is turned on drains a large amount of power from everything else. Is this normal? I've had a Corolla before and never had that happen before. Thanks

On the surface, it sounds like an alternater. I would replace it fast before it ruins your battery. It would make the car completely die soon though. It shouldn't charge at all if it's going down like that. I would take it to an Auto Zone or Advanced Auto and have them check your battery and alternater. That will tell you if it's actually bad.

I agree. First check to see if the battery is bad, then the alternator.

yea, first check battery, with a tester, see if the voltage is low. I believe somewhere under 12 is considered low. Or the generic way, which i cannot confirm is safe for our models is turn on the car and pull off the positive terminal. If your car turns off, then your alternator is going bad or is already.

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its 14.5 for a good and 10.5 for a bad that trick does work as long as you have an alt thats shot not going out what you can do is check the water level in the battery

A sitting battery isn't going to have 14.5V.
With the engine running you should have that at max.

Just checking the voltage won't give you a good idea of battery condition.
Have it load tested [pretty much any actual battery tester is a load tester].
Hatchys right about the water. If you have a battery that you can remove the vents check to make sure the electrolyte inside [water/acid] is up to the right level.
http://images.google.com/imgres?imgurl=htt...ficial%26sa%3DN
Make sure you use DISTILLED water, not tap water. It's just pure 100% H2O that you can get at pretty much any grocery store.

Also make sure BOTH battery connections are tight and clean. Make sure the top of your battery is clean too.

If the battery is ok, get the alt tested before you assume it's bad.
While it's most likely 1 of those 2 things, there is a chance it's something else.

check your battery terminals for corrosion, any crusties on the terminals can act like a load and absorb power under high load.

i think i may be having a similar problem. the battery in mine is new but i think the alternator might be going out. i don't think it is charging my battery up to a decent level. here's the thing. this is my second celica and i got used to being able to just leaving the lights on and they would turn themselves off after about 15 sec of getting out of the car. so i keep leaving my lights on and after 20 min the battery is allready dead. the switch that tells wheter or not the drivers side door is open or closed apparently is stuck and i need to get that replaced as well. it is really frustrating

My headlights dim when I am at idle. When I rev it I can watch my lights get brighter

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same happens with me. also, sometimes my radio n everything flickers off then back on again when i put on the brakes. i just recently got a new battery though so im prety sure its the alternator. it makes a little whisling sound as i rev too.

One more thing to check is the ground cables. There are three total. Disconnect clean and reattach them. My lights dimmed pretty badly when I hit the brakes before I cleaned up the grounds. A bad ground makes charging the battery much harder for the alternator. Better yet replace all the grounds with 4ga wire. Stock is 10ga and way to thin.

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on top of that you want to clean the paint from under the conectors