Tach install

[97Coro1.6]

I have a 1997 Corolla 1.6L. I bought a Sunpro tachII to install. I am having problems with the wiring. The install instructions say to hook up the green wire foor the tach to the negative on the coil, can't find the coil but found a green wire coming from the distributor. Tried to hook it up there, it works on that wire but when i rev the engine to let's say 4000 rpm the tach only rises to 1000 rpm. What am i doing wrong!!!!