Enable telemetry on : 
-------------
DIRT3 : 

Documents\My Games\Dirt3\hardwaresettings\ edit hardware_settings_config.xml like this

<motion enabled="true" ip="127.0.0.1" port="20777" delay="1" extradata="3" />

!!!!! Warning !!!!!
Dirt 3 Complete Edition telemetry and DIRT Showdown telemetry are broken and may crash at the beginning on the end of the race :

Thanks to RoccoC a fix is available here : 
Fix page : https://github.com/RoccoC/DiRTTelemetryErrorFix
download link : https://github.com/RoccoC/DiRTTelemetryErrorFix/raw/master/bin/DiRTTelemetryErrorFix_Release.zip