1999 Volvo S80 brake lights on

Hi I have an odd problem .Maybe You can shed some light.Im working on a 1999 S80 the car had no previous problems.It sat for 6 weeks and the battery went dead .I hooked up a jumper box and let it sit for about 10 minutes before attempting to start and then left it hooked up for an additional 10 minutes after starting so the alt could ease into the stone dead battery.Every thing seemed fine till an hour later when the customer complained noticed the brake lights wont go off.I checked it over and cant seem to get them to go off unless I pull the brake light relay in the trunk. Any ideas. Thanks Mark Calim