Here are several websites that owners have found useful or very useful. If you know of any others that you have found worthwhile please email me the address and I should be able to incorporate them into this list.
A possible source of information is to search for, say, 'Vectra forums' if you own a Vectra into Google or whatever search engine you prefer. This tends to bring up quite a list of useful sources.
Think carefully about your car too - many manufacturers have links with others in the industry or share the development costs on specific parts which both then utilise. As an example - one may not think that a site for VW Golfs could have any direct interest for the owner of a Ford diesel Galaxy, but it might in certain circumstances - the diesel Galaxy shares many parts with the diesel VW Sharan which also uses some parts which are common with the VW Golf.
All makes of car Vehicle AC Information Website
www.customferrariparts.com interesting parts together with alternative part for common recirculation flap fault
Ford Probe www.ukpoc.co.uk
Parts for Probe www.fordprobestore.co.uk
Ford Focus www.ffoc.co.uk
Ford Scorpio Ultima www.fordscorpio.co.uk - an extremely good site for Scorpio owners - much information
Ford Galaxy/VW Sharan/Seat Alhambra www.fordgalaxy.org see also VW Golf below
Mitsubishi Shogun/Pajero www.pocuk.com
Nissan Surf www.yotasurf.com
Nissan 300ZX www.300zx.co.uk
Opel/Vauxhall Vectra www.vvoc.com
Trucks www.chrishodgetrucks.com loads of interesting photos of historic trucks and much other hgv based information.