Just new on here... but what i did (kinda hard to explain) was if you take the gauge cluster out:
The yellow circle and the green arrow are to help you get your bearings:
Green arrow = up
Yellow circle = the bulbs for PRND21
Not in the PINK circle is the ribbon type bit you wanna take out or put a slit in. It has 4 "wires" (dont know exactly what to call the ribbon type wire setup lol) one says 100k, 2 grounds im guessing and one says 10k.
So if you chop this it should work... ive done this to mine but the only catch is that i cant test if it works properly yet, as my speedo doesnt work cos the speedo drive in my manual box is an electronic sendout, as supposed to cable. I see this working, but conformation on this would be appreciated!!!
Sorry i cant be more help, but hope this does help in some way!