need help voltage problems

[MIKEY'S 2002 TA]

hi, i have a 02 trans am. i am having a problem with my voltage once my second radiator fan come s on. i have a new battery and alternator. it charges fine and the volts stay at 14 until that second radiator fan kicks on. then the voltage will steadily keep dropping down to between 10-11 volts. as soon as that fan turns off voltage jumps back to 13-14 volts. i know these fans draw alot of current when they are both on,but the car used to say between 12-13 volts. could it be the fan or the wiring going to the fans??? any input would be appreciated. thanks,mike

[davidws6]

If it was fine before, probably the fan motor is starting to fail.

Is it the same if you rev up the engine a little? If you have a 15% or smaller underdrive pulley, that will make a big diff. @ Idle..

However, I would not rule out the alternator. I had 1 checked 2 times and the parts store tester said it was good. Stuck it back on the car and boom, 14 volts, just for a couple of seconds, then down to 11volts again. I stuck a used alt. off another car on, solid 14 volts.