Hyundai Repair: Hyundia System Low Voltage, slow blow fuse, battery cables

Question
Hello Sir
I am getting the code PO562 low system voltage on my 1998 elantra. It all started 2 weeks ago when i was driving the radio shut off and then when i pulled into the store the car shut off and won't start again. I tried it 15 minutes later and it started fine and then started to die again but it seemed when i got up to highway speed it would work better. I have a dashboard clock that i watch it would go dim its seems when i was at slower speeds and brighter at high speeds.  It also seem i can drive the car to work in the morning and not have the clock dim but when i leave to come home it dim within minutes. I had the altentor rebuilt about a month ago. I checked the ground wire to the fender and took battery cables off and cleaned them. Thank you for your time any help would be great thank you  

Answer
Check the main 100A slow blow fuse.  If okay, your alternator is probably still having problems.  

To check for certain, unplug the alternator connector and turn the ignition on.  One terminal should have battery voltage and the other (the battery lamp circuit) should have 7 to 8 volts or so.  If this is okay (and your belt is tight), your alternator is still not charging properly.