was driving my 03 Evo VIII and a week of raining and all of a sudden the battery and brake lights come on. Not a steady brightness, but a dim flicker and eventually goes off. Checked both battery terminals, fuses, and brake fluids and lines. No issues. Any suggestions???

 

Assuming belt isn't slipping of course....Check charging output at the back of the alternator. If it is NG, alternator time. If it is OK, check your cables again.
Bat/Brk at same time is triggered when system voltage dips below ~12.6V or so.

 

Have your battery and alternator tested; one or both are going bad.

 

so I checked the alternator, 14.4V. drove around for awhile and the battery, brake and anti-lock lights all came one. stereo started going out when I hit the brakes and eventually all lights, to include head, tail, and marker lights, went out. then all of a sudden all the lights came back on, the battery, brake and anti-lock lights all went out and the car ran fine. even restarted without hesitation when I got home. Confused!!!! will be checking fused and connectors for corrosion and proper grounds! any other suggestions??

 

same **** that happened to me bro. Its the alternator just change it out. It has its moments one minute you check it and its charging and the next day its not charging until finally just gives out.

 

Check your Alt. voltage with all loads on, AC, headlights, stereo. Also, since you said it was raining a lot, might not hurt to pull that kick panel by your left foot on driver side to see if that harness hasn't gotten all corroded up.

 

harness is good, voltage is good. think i found the issue. the brain for my alarm is "tucked" in that same area but not secured or protected from moisture. after checking that harness and cleaning the connectors and securing the brain in a better location, not warning lights and alarm is working properly. sometimes its best to do it yourself!!