the speedometer and odometer have stopped working

I have an old Fiat Tipo (L reg) Although the rev meter is fine on the same window. Help a couple of months ago the speedometer and odometer were working ok (although they had failed previously and then started working again). Now they just don't work at all, as I say, for a couple of months. The car itself is driving very well and other electrics including the rev dial work, petrol economy dial etc all work fine. My mechanic, over the phone but who has now gone away for a long holiday in India, said it is probably to do with the wiring going inside the bonnet but I can't tell or see what he means..to be honest I don't know where to look. Any help please? Many thanks. (I'm sorry I can't make a donation, I'm currently unemployed after a bad illness and on benefits).