Battery light comes on and all the lights get brighter

I replaced my ecu today cause the old one had a burnt diode in it. The car runs fine other then ive got one problem. The battery light comes on with and without the headlights on but the weird thing is that when the battery light comes on all the lights get brighter. The headlights and the dash lights get brighter when the battery light comes on. It doesn’t stay on all the time though. It comes and goes randomly, sometimes coming on and off several times in a row for about 5 seconds. I know the battery has plenty of charge and the alt is good too. The battery light was coming on before i replaced the ecu so it’s not the ecu causing it. The car feels like its drving in sand when the light comes on, like it doesnt want to get up and go, but as soon as the light goes off the car picks up and goes just fine. I just don’t understand why all the lights get brighter when the battery light comes on. Any idea guys, i need help and i’m afraid that it might cuase the new ecu to go bad too. Thanks

the battery light only comes on when the ecm detects an irregularity in charging voltage. ie your voltage regulator is probably pooched. this would explain why you get brighter lights when this occurs (higher than normal voltage). you should repair this asap, otherwise you could damage components

well crap i bet thats not cheap. thanks for letting me know man, least now i know what to be looking for. is there any way to plug something up to it to see if its not working properly?

Sounds like over-voltage to me too… The only way to really tell is to hook a volt meter to the alternator and see what voltage its putting out.

The red lead form the volt meter should be clipped to the positive cable on the alternator (the cable that is held on by a 10mm nut) and the black lead should be clipped to the negative battery terminal. Proper alternator voltage should be 13.5-14.5V. If it is higher than that then your alternator (voltage regulator inside the alt) is bad.

But the battery light would have to be ON when you do this test, otherwise it will probably read normal.

I hooked up a volt meter and when the battery light is off it reads 14.something and when the battery light comes on it jumps up around 20. So I need a new alt again. I’ve only had this one for not even a year, but its a lifetime warrenty at auto zone so i’m not trippin. I just wont drive it until i get the alt, I don’t wanna fry another ecu or anything else. Thanks for the help guys.

Good stuff, glad that the problem was found… There’s nothing worse than trying to diagnose a problem and not finding anything conclusive lol.