I have a 92 grand cherokee. the battery tested good and so did the alternator, but the parts store said the charging system isnt working properly. sometimes it the battery guage reads as if its ok and im able to drive around. sometimes its just above the red and slowly works its way down. i've no clue what to do... anyone got any ideas?

 

May have a voltage regulator problem. It is built into the SBEC (engine computer), you see the output of the alternator with a scan tool and see if it is charging.

 

It's probably in the wiring then. Trace the cables/wires that come off the alternator. If anything looks suspicious post up a pic. If something is totally FUBAR then replace it.

 

i had the same issue i must have pulled that alternator out 4 times to get it tested and it always passed i just didn't get it i decided to buy a new alt and it fixed it