How to prevent well intended project managers from getting too involved in the details? When working on projects, there are often Project Managers who have transitioned from technical roles. For better or worse, these project managers often take the lead in defining the technical deliverables often at the risk of alienating the technical teams, missing dependencies, constraints, etc that define technical achievements, etc. Sometimes a project manager comes along who has had basic exposure to technical solutions and attempts to define technical milestones. Rather than then tell them that it isn't their place to define these (since it can result is unintended results e.g. conflicts, challenging egos, etc), what would be an appropriate approach or sets of approaches?

There are certainly people who cannot help jumping out of their swim lanes and getting involved where they should not be. When that happens, you hit that head on and let them know they are interfering and jeopardizing success. The PM, however, has license to jump out of the PM swim lane and you cannot tell him/her to leave you alone.

Assuming you do not have a chronic, micro-manager type manager, your PM is jumping out of the PM swim lane because of you and your team. It's not the PM and the solution is not to figure out how to handle the PM. It's you and your team and the solution is to figure out what your team is doing or not doing that is causing the PM to interfere. There is a lack of trust, a lack of performance, growing risks, complaints, something.

If you have that micro-manager type PM, then be happy that projects have an end date, at which point you can find another project and another PM.