I'd start by using the instruction sheet that should have come with the denso..unless you sourced it used and don't have it for some other reason. All of the newer denso alts I've seen, including the one I put on my 68, have a main large stud for pos 12v and then spots for 2 more wires. those are for the field wires coming from voltage regulator. I say spots for those other 2 wires because depending on year, some have just 2 studs, others have a socket that you need a special plug for. accomplishes the same thing: connecting the 2 field wires to the alt.

This is all speculation based on assumption here. What model denso? do you have a pic of the back of it? There's more to it as far as upgrading wiring if the denso is high amp... also depends on whether you are keeping the wiring in the car stock 68 single field or later dual field....that changed in 69 or 70, I can't remember.