r111yun, do a search on the forum, you can get a microswitch from Maplins for less than a fiver, drill out old one and pop in new
Did this recently and only took about thirty minutes (but check you wire it up correctly).
Yes, I wrote about that, can't remember where though!
There are two more of these little switches to be aware of - one in the Spider roof mechanism (passenger's side) which disables the air conditioning when the roof is open. The other switch is in the boot lid latch, and operates the boot light (and probably the check for when it's open). All mine were broken; have fixed the bonnet and boot light but not the roof one yet.
It is nice to have the bonnet switch working properly for two reasons - if you have the factory alarm (in right-front wheel arch), it will reduce battery drain (there's a relay on all the time otherwise), and also it's nice to see a red light when the bonnet isn't latched properly rather than finding out some other way (seeing it flutter at speed, or worse).
I liked the bonnet arrangement on one of my first cars (FIAT 128) where the bonnet opened forwards - great idea - Honda did it for a while too. No need for a safety catch, and if the engine was overheating you could just let the bonnet float in the breeze for a while.
No such luck with my Lancia Thema and the self-jamming catch with broken micro switch. Being of the usual backward-opening type, the bonnet didn't float in the breeze - broke the windscreen and damaged the roof, writing the car off beyond economic repair. After that's happened to you, it makes you appreciate that red check light...