Green and red conductors of the 4-conductor cord are actually for the receiver circuit only.
You may want to remove the receiver unit and measure the resistance across the two contacts on the back. It should be about 26 ohms, and you should also hear faint clicks from the battery in the meter. If not, the receiver is probably open (defective).
If it's good there, then replace reinstall the receiver unit, and measure across the R and W terminals inside the handset. (If not, then either the two contact springs in the handle are not making good contact with the receiver, or the wiring inside the handle is bad).
If still 26 ohms there, measure across the R dial terminal and W dial terminal, i. e. , where the handset cord is connected. (If not working, then the handset cord is open.)
Next, leaving one probe on R, move the other from W on dial to BB on dial. (If not working, then the bottom two contact springs of the dial are not making.)
Then move probe from BB on dial to W on hookswitch.
Then move probe from W on hookswitch to GN on hookswitch, with the handset out of the cradle.
Last, move this probe to the green conductor on the loose end of the cord, and the other probe from R on the dial to the loose red conductor.