It should be in place from the factory.
Otherwise, there is a blank plug in the block which is removed and replaced with the heater.
Connecticut has a similar temp to you and mine starts like a charm after 30 min of heating. [Of note, I did recently replace the 5 glow plugs and the relay]. I have a switch to my garage in the house so I flip it on when I know I'm going somewhere.
'83 300D-T 150k