My 1984 300TD Turbo won't shut off with the key anymore, so after researching the subject here, I took these steps:

1. tested the shutoff at the IP. It works.
2. the vacuum pump makes @17" Hg vacuum (520 mm Hg) at idle on the main line before the brake booster.
3. the brown shutoff line that goes to the ignition shutoff solenoid tested at 115mm Hg vacuum at the firewall. It tested at 200 mm Hg at the solenoid on the ignition switch. the brown line is on the outside nipple of the solenoid (don't know if this is right).
4. The brown striped vac line on the inside nipple of the ignition solenoid tested at zero mm Hg vacuum.
5. I replaced the ignition solenoid.

The engine still won't shut down with the key. Any ideas?