gauges work only when revving

well after charging my battery to 14.89V i then started the car, every thing worked the voltage at the alternator was 14.4V, same with the battery. BUT.. after about 5 min, after the oil heated up the rpms dropped a bit from 1300RPMS to just under 1000RPMS... the voltage started to drop guys.. and i mean drop!.. from 14.4V at the battery and alternator to 14V, 13.87V, 13.25V, 13V 12.8V etc etc i quickly turned the car off. so what it looks like, whenever i rev the motor voltage rises again.. stays like that for a bit then drops.. its looking to me like the alternator cannot charge at low rpms and only high ones.. so you guys were right im in the middle of changing my alternator now. AGAIN back to the stock one.. then im gonna take that "160A" out and get it tested at as shop in the GTA.. and to top it off , i go to put the other alternator back in, and theres slack on the line! i cant get rid of it.. blah ! ill keep u guys posted

I strongly suspect a bad battery - your alternator may be ok. Charge the battery and then watch its voltage drop. Maybe first connect a load (headlights etc) for a few to 15 minutes to remove its surface charge to get it to ~12,7V open circuit (no load). Then ensure it remains open-circuit/disconnected. If the voltage drops, it's bad. If it drops 0.1V in 24 hours, it's badly stuffed. It should take at least12 months for an AGM battery to drop a total of 0.5V to 1V from fully charged.    But with a 160A alternator, that Optima should get pretty hot. That's how an Aussie Richard Cranium finally figured out that his post's first reply was correct - his 3-month old Optima Yellow was stuffed. Unfortunately 4 more pages and several LONG PMs didn't convince him, but the HOT battery did. (He upgraded a 45A alternator to a 75A alternator because he thought the alt was the problem. Dik Hed indeed!)

well gentlemen, i left the car over night and came back in the morning and measured the voltage and it was 12.6V. i was reading up & contacted optima and they said that when the battery is discharged it takes a few recharge cycles to re-energize the electrolytes in the battery again. now whats funny is, i take out the 160A alternator and i look at the pulley and it has an indentation!!! the belt was just starting to rub!!! luckily it wasn't on the car for long so the belt is still good. now i do some testes on the alternator, i find out at; 1000RPMS its producing 3.3A 1500 - 23.3A 2000 - 29A thats where my issue is!! the alternator!!! the alternator is only good at high RPMS.. i loose in the low RPMS.. so what ive decided to do is.. make the pulley smaller on the alternator so it can produce better amperage at lower RPMS.. also i'm going to recheck the regulator. i noticed now that when i put the belt on the alternator there was 1" play in the belt even after adjusting it! so i've decided to bring the size of the belt down one notch to make it have the perfect play in it.