Removed the dash binnacle to trace pipes, the two main brown pipes appear to connect to the ignition switch - I can be 100% sure as going by feel only, but there's nothing else around that area needing a vacuum.

Is it usual to have two pipes connecting the ignition switch?

The other two marked 'a' in the diagram just sit behind the binnacle itself, the spare 'c' appears to be as above, hooked up to the ignition.

The vacuum noise above - doh! moment, as the hood pad has been removed allowing a big gap between the bulkhead and hood allowing engine noise into fan duct, or at least I hope that's what it is - everything gets amplified through that horn ..

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)