My 2.5 electric/heated door mirrors

Have fitted electric / heated door mirrors to my 2001 NB 2.5 FL.All the wiring is in situ to make the mirror movement work ,however there is no power to the heated part .I have tried the usual method of switching the HRW onto no avail. I have checked with every wiring diagram I can source but nothing shows the wiring circuit for the heated section .Is there anyone out there who has experienced the same problem ?