Make sure you have good fuses and that you didn't fail to connect something. I'm not sure where all the wiring is on the W123, but it's very possible you pulled something loose while changing the engine.

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!