GREY Wire is your signal from the PCM------- Goes to WHITE wire in tach
1st BLACK wire is the 12V ignition hot-------- Goes to RED wire in tach
(FSM calls this "red")
ORANGE wire is the dimmer light -------------Goes to GREEN wire in tach
2nd BLACK wire is the ground----------------Goes to BLACK wire in tach
Now, to add to the confusion: If your tach doesnt work with the wires hooked up as noted, you need the adaptor plug in from ISSPRO (I bought mine from a TDR advertiser for $27 shipped to my door) that has the correct filter in it to reduce noise from wherever noise comes from. Mine woked in my truck AND Mom's truck. Helped diagnose a sloppy torque convertor in hers (I had told her that, but now I have numbers to quantify it).
Daniel