2005 Ford Freestyle

I was cleaning my car tonightand had left the engine running with the A/C on. Evertime time the fan turned on the idle would drop as if the car was going to stall. Now when the A.C is off the problem disappears.

When I was driving home it seemed to get worse. This time the lights where flashing also.

Once home while the car was parked in the driveway the backup lights were actually flashing on and off in time with the activation of the cooling fan.

Does this sound like a alternator problem or some other electrical problem?