this just started a few days ago. when i am decelerating and i step on the brakes, all my lights dim and the radio turns off, it seem like the car is about to shut off.

when i accelerate and brake its fine, when i am stopped and brake its fine

i havent change anything on the car for a few years now.

 

Check your altenator, if its bad replace it
And get new bigger engine grounds. I be it you do both the problem will dissapear

 

i had the same problem, when i was on the brake and stopped i idled at 100rpms , every thing dimmed, then when i let the brake of it when bad to normal, so i swaped the engine (cuz it was a d15b2 to a jdm d15b) and it was all better

 

and it had a dif altenator on it to i presume?

 

can you take a video of this? haha sorry i just think that would be interesting to see...ill shut up cuz it'll prolly happen to me now

 

Clean the battery posts, connectors, and ground wire thoroughly. Then check whether the alternator belt is loose. If not, take your car to an auto parts store that will check the alternator and battery free of charge.

 

x2
if anything the alternator is probably wats keepin it alive.. usually your car will already run off the alternator and your battery will get recharged by the alternator.. your battery is usually there to help start the car and power on a few things but that is all.. I would also look into grounds or possibly a look battery connection or clean battery post as RONJ@HT has stated