1989 bowrider: Ignition starts but does not stop the motor

Hi all. I bought a 1989 18' doral with a 140hp OMC in/out and I've been fixed it up but I've run into a curious problem. Once we checked that it would start and run, we took it out for a good long run, primarily to burn off old gas, but the motor wouldn't shut off after I turned the ignition key to off. I even removed the key and the motor kept running. We had to choke it down to stop it and figured that the ignition was faulty because the first few times I started the motor in my yard, it started and stopped with the key. So I bought a new ignition and replaced the wires exactly as they were (I used tape to mark each wire in a unique way to ensure they didn't get mixed up.) The old ignition only had 3 contacts for B I and S while the new one has the additional A(ccessory) contact and i was certain that I put the wires where they belonged, but it did not solve the problem. Does anyone have any experience with this, or know what I can do to resolve it? I can't risk taking the family out until I know the boat starts and stops reliably, so I would really appreciate some help. Thanks! Darren.

You will get better responses if you post this question on the OMC forum on this site.