Have soemone engage and disengage the OD while you listen under the
car. No click at solenoid:

Use a volt meter to test for voltage at the solenoid. They are
inexpensive at just about any X-mart (like $8-12). Handy to keep in
the car anyway to test for voltage and test bulbs and fuses and such.

Removing the lead from the solenoid and using a 12 volt source you can
energize it to see if it is operational.

If the solenoid is good and thee is no voltage there then check the
relay.
            __  __
    Randy & \ \/ /alerie's
             \__/olvos
'90 245 Estate  -  '93 965 Estate
  "Shelby"     &      "Kate"

Is this automatic or manual? Assuming automatic, the relay is 95% likely
to be the problem given the symptoms you're seeing. It's located behind
the dash to the left of the glovebox (LHD cars) and is most easily
accessed by removing the glovebox assembly. Once the relay is out, the
cover can be popped off and on the circuit board you'll find cracking in
the solder joints at the heavy connections, this is the problem and it's
fixed by heating the joints and flowing some fresh rosin core solder
into them.

Look for a round single wire plug under the car, on the passenger side
at the rear of the transmission. With it unplugged the transmission
should shift into overdrive normally. The odds are about 3 in 10 that
the solenoid is at fault. The other 70% of the time there is a problem
in the valve body in the transmission, especially if the fluid hasn't
been changed regularly or has gotten low. There are several nylon check
balls the float up against the separator plate in the valve body that
can erode away to nothing over time when the fluid is carrying a lot of
metallic debris.

Bob