Trouble installing 39-315 key lock

Thank you for your patience during this busy season. In answer to your question, the tail on the internal thumb lever goes into the same mortise slot as the tail on the 82-315 key lock. They should be in the same position. Do you have your old handle still available? If we can see that, maybe we can come up with a solution for you.

This looks like a standard 82-035 handle and 82-218 mortise. Looking at the hardware you have here, there's no reason why the 82-315 shouldn't have worked. Everything here is fully compatible. I'll need more detail on exactly where you're running into issues.

That's the mortise lock, which matches our 82-218; the 82-218 and 82-315 that you purchased are 100% compatible. It's one of the most common combinations out there, in fact. There must be something else that has gone wrong, but I don't know what it is based on the given information.

Your old handle set resembles our 82-035, which is designed to be used with the 82-315. This is the hardware you need, without a doubt. I'm just not sure why it won't work for you.