fitting a kenwood dv3200 sat nav

[bjdp]

i have a e30 convertible 1988 m20 engine.. i've fitted a kenwood dv3200 sat nav but can any one help with the attachment of the speed wire as i dont know were to fit it. plus my spped wire hasnt got the "portection diode" on it(been cut off) that the kenwood manual says it should have??? any ideas on were to get this diode,or replacment one, from
cheers guys......brad