97 Cefiro Wiring help

I wish to put a Speed Alert monitor into my 97 Cefiro, which has to take its signal source from the pulse generated from the gearbox and received at the electronic speedo unit. I am unable to identify which wire is the correct one so need a wiring diagram with colour codes. If any one can help with any details or a photocopy of that section of wiring ( around the speedo unit) I would appreciate any contact.