For the SAAB aficianados on here I've just put a post up on SAABscene as to resolving this problem. Turns out it was the oil pressure sensor leaking. Impossible to see as it's buried at the back of the block behind the starter motor.
Cheap to fix in terms of cost c.£7.50 but a right swine of a job.
HTH or U2U me for further help.
Cheers, Pewe

out f interest where did you get the sender from?

Ashg, Whitequay Alfa Romeo in Reading (local SAAB main stealer) tel 01189509000 p/n 55559824 LP0195Switch Oil £5.96 + VAT.
Cheers, Pewe