Greddy Turbo Timer fitting

[dturpin]

Hi everyone hoping for a bit of help.  I have just brought a Greddy full auto turbo timer for my fd from TRex (cheers mate).  I have managed to find the fitting instructions off the Greddy web site, the only thing im not sure on is it says about connecting the TT up to the cars speed sensor wire.  Was hoping if anyone had fitted one the could tell me where the best place to find the wire would be? Any advice greatly appreciated.