I'm finally in the same boat (although mine has no hazards to worry about). Did my last bit of oily work at the weekend (oil + filter change and box/diff/grease lube). Now I am in the tidy and make pretty phase. It is ready for another winter of snow !
It appears that the fitting of hazards on a series 3 is more hassle than its worth there appears to be no simple way and no wiring diagrams. As there not required for a MOT I may well forget them just would be handy to have them. Need to sort brakes and steering!