hi all

im new on this site and only just got my first astra what i would like help with is fitting an after market head unit as i do like my music 

my first option would be to fit a sat nav unit like the alpine ine w990bt this requires a speed pulse signal for more accurate position on the unit where would i find the speed pulse wire to tap off??

i could forget sat nav and go with an alpine ive w585bt to fit both of these i will need to change the fascia is this a pig of a job or not to