It looks to me like you have it hooked up correctly.

I make aftermarket 66 charger tach boards. I will upload the manual I wrote for my tach board as it has some information about how to connect things. You will have to ignore the parts about adjustments as those are specific to my aftermarket tach board.

By the way, I sell my board for $75 plus $10 shipping if anyone needs one. I am in the process of coming out with 67-74 tach boards as well. My board fits inside the original sending unit can, so the originality of your car is maintained. I use modern electronics so you don't have to worry about the board going bad on you like the original boards.

As far as the wiring harness, you should be able to splice into the hot wire. But you will have to run the wire that goes from the coil to the sending unit, and the wire that goes from the sending unit to the tach.

Sometimes you can fix the old sending units, usually the capacitors are dried out. I have also seen a few with fried transistors. I have seen some with fried transformers, and these would be very difficult to fix.

P.S. I tried to attach the PDF file, but moparts only allows attaching pictures. Here is a web link to my tach board manual:

http://www.rt-eng.com/mopar/TachBoardManual.pdf

Greg Garner