Just a little follow up. On my 780 B280F wiring diagram Volvo shows
that the red wire marked terminal 1 on the crankshaft sending unit
goes to terminal 10 on the ECU. The terminal marked 2 on the sending
unit goes to ECU terminal 23 (blue wire). The terminal marked 3 on the
sending unit (thick black wire) goes to terminal 11 on the ECU, but
the picture shows it grounded inside the ECU.
I am getting an open circuit between all terminals on the sending
unit, except between terminals 1 and 2 (blue and red wires). I get an
open circuit between the ground wire and the others.