Battery and Brake Lights flash when i accelerate.

[haish1023]

hey how are you guys doing? my battery light and brake light on the dash both blink and sometimes stay on when im accelerating , especially one the high way, i went to the mechanic because i thought it was the alternator, but they tested both my alternator and battery and both of them are good, any idea guys be4 i go to the dealer and they try to kill me with there prices.

[MinisterofDOOM]

Alternator is probably the cause, despite the fact that it tested good. Bad alternators will often test good. You have to catch it acting up during the test, which is difficult. I've dealt with far more bad alternators than I'd like to have dealt with and most of them never actually tested bad. But they were definitely bad.

[haish1023]

Thanks man, you think i should wait until it really goes bad to change it or? or change it now?

[MinisterofDOOM]

I guess that depends on how you want to deal with it. If you're getting battery and brake lights, it is probably bad, which means it's not charging the battery properly. That means sooner or later the car is going to refuse to start. If you wait, you'll most likely end up stranded somewhere inconvenient with a car that won't start.

Either way, keep a set of jumper cables in the trunk if you don't already have them. You'll probably need them. But if it were me, I'd definitely change it now rather than later.

Also, try having the alternator tested off the car. Those tests are more accurate (but still nowhere near foolproof). If you need to convince the parts store it's bad for warranty puproses, that's the route to take.

You can run a simple test yourself if you have a multimeter. Next time it starts showing symptoms, stop the car somewhere convenient and test the voltage at the battery terminals (with the car still running). If the alternator's good, voltages should be 14v. If you're only seeing 12 or so volts, that's a good sign your alternator is indeed bad.