I have a 2009 Subaru Forster, the model with out the turbo. The battery light flickers as well as the head and cabin light dimming at the same time. This normally happens when driving over 3000 rpm but sometime happens below 3000 rpm. I hooked a multi meter up while driving and it seem to sit at 14.5 be I got a couple readings of 13.5. I don’t know if my multi meter would be able to pick up the voltage drop since it seemingly is jumping very fast. When not started I get 12.4 so In my mind that battery should be fine. I replaced the alternator twice now and it did not fix the problem. I also just changed the battery. If anybody has any ideas for me to try and hopefully diagnose my problem it would be greatly appreciated.
Have you checked the serpentine belt for wear?
Check all grounds
Check all wire connections to and from alternator and battery
I suggest you check for a voltage drop on the main cable to the battery. Place your meter probes on the main output lead of the alternator and the positive battery post while the blower and lights are on high and the engine running around 1500 RPM. You should have less than .3 volts of voltage drop if the connection is in good shape. If that is good then check the main ground wire the same way except use the negative post for that test. Check the chassis/battery ground. If haven’t already cleaned the battery connections so they are spotless you should do that.
Thank you guys so much for your help. I replaced the alternator plug as well as the belt and the problem is fixed. You guys are awesome!