That should be the spring that holds and returns the key to posII after turning it to start. EDIT: Progably not, as the switch is completely enclosed.

EDIT: Dealers order from the factory, but the parts are flown to the dealer. I would expect 2-3 days.
Remember the ball peen hammer and punch if you are going to replace the key lock.

When you turn the electrical switch to the right with a screwdriver, check the dash lights, if they all come on (posII) turn it a bit more slowly and see if the starter engages. If you feel resistance, then the spring came from elsewhere - probably the tumbler. Remember, you need to be in P or N to start the engine.

There is the possibility that the key itself needs to be turned a bit to engage the security ring antenna...

What ever you do, do NOT disconnect the wire bundle as the wires are not all standard colors and will be almost impossible to get back to the correct positions.
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My back feels better when I sit in a Volvo seat