New alternator...sat nav flashing, radio fading in & out

Hi, I need your help. Just had alternator replaced on 2005 Disco 3. 10 seconds after starting Disco sat nav flashes, radio fades in & out and an orange 'P' Lights on the dash. It doesn't last for anymore than 30secs and doesn't seem to have any other impact. Have tried a hard wire reset and had the battery load tested. Prior to alternator quitting the Disco was lighting up the dash like a Christmas tree. I'm no mechanic so your help is much appreciated. Cheers, Wayne

When your alternator failed some systems may have introduced low voltage related errors which may need clearing with suitable diagnostic equipment.