This is the sort of relay you need, available in any good car accessory shop or at Maplin http://www.maplin.co.uk/40a-spno-and-30 ... elay-37526
I've looked on maplin for a suitable diode but the on line selection is very limited. This one http://www.maplin.co.uk/6a-silicon-rectifiers-46413 is the highest currrent rating but it could do with being 10Amp to be safe. I'm sure that it you ask in an actual store you will find they have one.
