RE: Yes or No

I want to turn on an operation or turn it off by entering Y for yes or N for no. And when it is turned off be able to manually enter my own number.
This is the formula I used but it doesn't work;
=IF(L14="Y",(1+L9)*K12,IF(L14="N",0))

This doesn't work...

L12 is the active cell
L9 is where I will enter a percent such as 25%
K12 will contain an existing numberthat I want multiplied by, say, 125%.If I enter No then I want to be able to enter my own number in L12.

Thanks

Jeff