Boost signal line runs from the center of the manifold just about right above the ALDA to the switchover valve on the firewall, then to the ALDA and the transmission vac amplifier. White plastic line.

Check for integrity of the rubber connectors and clamps. Make sure the switchover valve is clear and doen't leak out the top when not engergized.

Peter

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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!