That seems to be a common fix for the failure. When I was looking at xj's, I saw 5 or 6 that had a starter button wired straight to the starter. Just yesterday, there were 3 Cherokees with that mod in the jy. Check your neutral safety switch. That might be your issue. There are some good write up's here on it. Search for NSS or neutral safety switch.
Volunteer, American Society of Military History. http://tankland.com/
Just got a 1989 YJ too!