Electrical System Problem

I'm having a problem with my electrical system, while running the system runs good and stays right at 14volts, but as soon as my rpm gets below a grand it immediate drops to about 9 volts. I have tried two different alternators so that is not the problem.

Any help would be greatly appreciated.

Welcome to af.
What year and engine?
Get a charging system check with the alternator on the car and engine running with all all stuff turned on.
Check alternator output amps for specs.
The charging voltage should no go below 13.5-14 volts engine running.

Also check battery and battery cabels

Certain faults with the rectifier bridge, inside the alternator, will cause the alternator to produce the proper voltage but insufficient amperage. This can cause voltage to drop at lower RPM. The voltage regulator is what turns off the battery light on the dash; provided the regulator "sees" proper voltage, the light will shut off. It's very possible you have a faulty alternator. It must be checked for proper charging voltage and amperage output. Some of the auto parts stores testers do not do a comprehensive test of the alternator... as MT mentioned, it's best to have it tested while it is on the vehicle. Also, a weak cell in the battery could cause what you're describing, (unable to take and hold a proper charge).