heroo, new here...just picked up a 87 montero has a problem im hoping someone gimme some insight on.

After replacing the starter...it will crank over but only if I run a wire from the postive terminal on the battery to the white/black wire on the ignition switch and a when its running it will only stay running if I hold the key between "start" and "on" I got a new igntion switch but I still need to jump it....any help would be greatly appreciated.