The rectangular fitting is for the engine temp sensor, which should be in the intake manifold water passage near the front. The single wire is for the thermo/time switch for the cold start valve. You can run without the thermo/time switch, but you really need the temp sensor connected or it will run WAY rich!

Check the wires to the sensor in the air horn as well, it will run way rich if that one is dissconnected, too!

The idle may work better with both temp sensors connected... If the one in the water passage has been removed, you really should replace it before driving any distance.

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!