1997 BMW Z3 Electrical Problem

I have had my BMW Z3 for 3 years and everything has been great, up until this last week. Installed a aftermarket radio a year ago with no problems.

Symptoms:
-Put the keys in and turn the car over, and the Multi-Information-System (time, temp, mileage) resets.

-Driving with radio on, and ac on, randomly the ABS and traction control lighting would come on momentarily. Came on and off 10 times within a 15 minute window of driving. Never stayed on for more than a second.
-In association, with these lights coming on, the odometer would dim, radio volume would dip, and AC fan speed would dip.

Any suggestions would be great. Thanks.