I posted this on another site and figured that is might help some of the folks here too.
Let me start by saying that I assume no responsibility if you try to do this. I am not an engineer or professional fabricator, just an average guy that knows how to build stuff and asks a lot of questions when I don't know what I am doing. But I am willing to help where I can. Feel free to ask any questions and I will do my best to answer.
Well I did a lot of research online before deciding to make the conversion from console steering to tiller steer and was disappointed that I was not able to find any information regarding the swap. So I figure I will post what I found in hopes that it might help others making the switch. I spent a lot of time on the phone with Steven's Marine, Three Rivers Marine and Northwest Marine and Sport to get this information, with Steven's Marine being the most knowledgeable. I have a 1986 Mercury 150 2 stroke and can make no guarantees as to what models this will work for. That being said the tiller handle that I bought for my motor is the same that is on my buddy's 2005 200hp Mercury, and it looks like it mounts the same.
My first question was is there a bolt on kit? The answer is yes, but Mercury is pretty proud of it and charges $900 for it. So I decided to see what else is out there. Keep in mind that you are going to need to have the ignition key switch, run/stop switch, and power trim toggle switch in the box that the handle mounts to. I was told that the tiller handle used by Steven's Marine was the handle off of a Mercury 90hp 2 stroke. After a lot of calling around I was able to find one in Florida and got it for $400 shipped. They even made me 2 new keys for it and put on a new throttle grip. I was told that any year will work because that part number never changed, I have not confirmed this though. Also at some point Mercury changed the connector for the wiring harness on their engine. I was able to find a tiller handle with the old style connector that was on my motor. I was told that if you can't find one with the same plug there is an adapter that can be bought for $50.
Well how do you mount the handle to the motor? If you look at your motor below the motor cover right above the transom you will see a metal bar coming forward off of the swivel bracket. This is the same bar that the hydraulic steering bolts to. you will have to make is or have it made. I was going to make it myself. I took all of the measurements and drew up a design. Then a buddy of mine that works at a machine shop said that he would do it for me and that they already have the materials. Freebies are sweet. And I should have it by the end of the week. I will post more when I get all of the parts and get it mounted.
So this is what $400 gets you

Here is where the ignition and power tirm is located

This is where the handle will mount to the motor
