The banjo bolt (rear of manifold, point to passenger compartment) can be cleaned. Small passage, tends to get clogged with age. Check the line too -- you must be able to blow through it (disconnect it at the switchover valve).

Not sure where the switch is, but it is the only electrical connector on the manifold. On my 300D it is right beside the boost signal line, but that is a 603 engine, not a 617. Probably in the center somewhere if not immediately adjacent to boost signal line.

The switch must be open at normal pressure and closed at about 15 psi. The only way to test is to check for continuity -- if it is closed at atmospheric pressure, replace it. You would have to apply 15 psi or more to see if it closed.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!