Yes I think the fuel pump relay or something associated with it (might vary
depending whether the car has much in the way of emission control add-on's
or not) needs to see 12 volts on a certain wire to tell it the engine is
running to keep the fuel pump going otherwise it will cut out. My 1985 900i
is set up like this. Turn the key to 'run', then the fuel pump starts for a
few seconds before it stops again if I haven't moved the key to 'start'.

The fuel pump in my 1983 900S doesn't seem to do that though - whenever the
key is in 'run' the fuel pumps continues going even if the engine hasn't
been started. That would well be a wiring fault or simply an artefact of the
build year. The 1982/83 C900's seem to have been caught in the middle of
some big transitions in ingition system design, etc.

As an example, my car, despite being a '1983 build' (Sep 1982 contstruction
at Trollhattan, early 1983 fitted with Australian compliance plate), has
points ignition. Only the C900's sent to the USA received hall-effect
ignitions from the 1982 build year up according to the senior tech at Saab
Serve where my car is currently having some work done on it so it can pass
rego. C900's imported to Australia didn't get hall-effect until the 1984
build year.

Also, only the C900's sent to the USA with 8V engines have all the fancy
emission control electronics that the Bentley manual talks about as living
under the rear seat. None of the 8V C900's imported to Australia seem to
have that. Don't know what the story is with 16V C900's though since they
were a totally different design in terms of emissions and emission control.

Regards,

Craig.