cfinney:
First, welcome to our Forum............
The 149 did NOT come with a four prong Ignition Switch. Thus, if you have one, it is the wrong switch.
Here is the correct part for your Tractor..... P/N:
IH-60736-C3
Here is a simplified Diagram for the 1x8/9 Ignition Switch
Legend....
Off = No Contacts Made
Run = B + I
Start = B + I + S
PS:
If you post a picture of the switch you got, along with the Brand Name, Part Number, and terminal identification, we maybe able to make what you got work.