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The battery warning light on this vehicle will only come on for one of two reasons either that wire going from the instrument cluster and light itself to the alternator is getting shorted to ground which would be extremely unlikely and virtually impossible or the field circuit in the alternator is not charging. How the system works is the gauge fuse sends 12 V up to the cluster through the indicator bulb then back out to the connector at the back of the alternator. Within the alternator if it is not charging current the field circuit that allows that voltage to go to ground thereby causing the indicator light to illuminate. Once the alternator starts to produce current in the field circuit voltage is fed back that line which negates the circuit to ground and causes the warning light to go out indicating that the alternator is charging. Either the shop did not check this correctly or when they looked at it it was charging. The bot***** *****ne is 99% of the time this problem is resolved by replacing the alternator. Make sure you buy quality alternator I've gone through two alternators because they wanted to go cheap aftermarket and found that the aftermarket one was not working correctly. Once I installed a good remanufactured Toyota or DENSO alternator the problem was resolved.