Noise from fan running near firewall.
 

Heard a noise after shutting down engine key still on.Thought it was blower motor still running but no. It was coming from under the hood. Passenger side near firewall, black box with computer and diagnostic plug inside. Small round blower motor attached to side of box, running with key on engine shut down. Unplugged it and it stopped running. Plugged it back in key on and it started running again. Looks like it vents the inside of the box with electrical inside and computer.
Anyone know where to look for relay switch or sensor that controls it?
I don't think it should run all the time.
1998 SL500.
THANKS,
mstaglian@gmail.com