Help! RRC 200Tdi Speed sensor wire for navigation: where is it?

Hi group,

I want to install a navi system in my 1993 Range Rover Classic 200Tdi but I
can't find any information about a speed pulse lead.

Navigation was installed in a 1990 Disco 200Tdi before and that car did have
a speed pulse lead so I suggest my "new" car should have one too, but where
to find it and which color code should it feature?

Any help and suggestions much appiciated.

Mark
Holland