Porsche Repair: Motor cuts out, blown fuse, expert system

Question
I drive my car 928s 84 mod at just a cruse speed and
it just cuts out when I go to the fuse board on passenger side I find that a fuse has blown I replace it sometimes it lasts 3 months sometimes
it blows straight away and I have to wait for a while for it to reset? and acept a fuse!
I have had auto electricians look at & say its OK
the Question is what part could cause this? As I dont feel confident when I travel distance. Hope that you can help

Answer
Hi Chris,

Thanks for re-stating your question.  Now I understand your frustration.

I'm sure those mechanics and technicians know what they are talking about, but this is far from OK!

Could you answer a few more questions:

1.  When you replace the fuse, which number fuse and what amperage is it?
2.  About that blown fuse... what circuits does it control?
3.  Tell me more about replacing the fuse...when you do the engine starts right away and doesn't cut-out for three months, right?  And sometimes it blows right away.  If it blows, how long do you wait till a fuse will work?  
4.  And what do you get after it blows...the engine will crank but not start...or...no crank...or what?

Just use the Expert system follow-up process and give me some feedback...Thanks.

Dave