Do you have the overdrive hooked up per the diagram in the green bible? (page 194, fig.46)
If you do, block the wheels to prevent rolling away, put gear shift in any gear except reverse, turn the ignition switch to run (on), DO NOT start engine, short the govenor wire to a good ground and listen for a click from the overdrive solenoid. If you hear a click, check that the overdrive handle is pushed in all the way. (Out prevents overdrive). Also the lockout switch on the driver's side of the O/D tailpiece will prevent the click if open or the O/D handle is pulled out.
Do you have engine braking when decelerating below about 24 MPH? If you do, then the overdrive is either locked out (direct drive) or you are in full time overdrive. To determine which, monitor the engine speed in 3rd gear. If it is excessive at 70 MPH you are locked out of overdrive. If you seem to have about 2300-2700 RPM at 70, you are in overdrive. You would notice "in overdrive full time" when taking off in any gear--the engine lugs and performs poorly on acceleration.
If you have a "freewheeling" (no engine braking) condition above about 30 MPH you are not in overdrive. You need to check that the solenoid, relay, fuse, and kickdown switch are good.
To check various parts of the electrical system, short the govenor wire to ground and test for battery voltage at overdrive relay and fuse, then at the solenoid coil connection. If there is no battery voltage present at one of the test points, repair or replace the relay, fuse, kickdown switch or wiring as indicated. 1949 and 1950 vehicles with a stock overdrive had a lockout switch located on the driver's side of the overdrive tailpiece that must be closed when the O/D handle is pushed in or you are in neutral or any gear except for reverse.
If you have high engine RPM at 70 MPH and you have freewheeling, and all the other components are testing OK, consider a bad govenor switch or possibly a sticking internal part in the O/D.
There is a pretty good description of the O/D system in the green bible (1949-50-51 Ford passenger car shop manual) on pages 194 to 198.