Starter won't disengage

[Jasonlocke]

Hi there, I have read a few forum posts on this and tried a few things but still have the same issue. I have a 92 bayliner bowrider with a 3.0 mercruiser inboard. I recently had my starter rebuilt, and after reinstalling it, it ran great for one or two runs. Now, when I turn the key to start, the starter winds up and won't turn off without disconnecting the battery. I pulled the starter out, connected it to a battery with jumper cables, and jumped the two posts to get the starter to engage. It works fine when connected straight to a battery on the bench (disengages when I remove the jump). So I put the starter back in and reconnected everything. Went to start it, same thing, won't disengage. Removed exciter wire from starter, tried jumping it, same thing, won't disengage (without disconnecting battery). Removed all wires going to starter except for line from positive on battery. Same thing, won't disengage. I even disconnected the wiring harness in case there's a short somewhere. I'm not sure what to try next... any ideas?