On the fourth day of the flight of Apollo 9, Schweickart felt better than expected as he worked his way into the lander to get it ready for the EVA. By the time he had put on the backpack, McDivitt was ready to let him do more – to stand on the lunar lander porch at least.
Lunar Module to Command Module transfer procedure
Schweickart on the porch of the Lunar Module
Scott standing in the open hatch of the Command Module
As Dave Scott pulled in closer to the Lunar Module he noticed that the command module’s nose was out of line with the lander’s nose. Scott tried to use a service module thruster to turn left, but that jet was not operating. It turns out that someone had accidentally bumped a switch that turned off one set of Thrusters. The crew then flipped the correct switches, and the thruster started working, and at T+3 hours 2 minutes the command module probe nestled into the lunar Module drogue, where it was captured and held by the 12 latches. The first docking of the Lunar Module in space was achieved. As a side note, switch guards were installed on all future Apollo missions to prevent accidentally flipping a switch.
LM on S-VIB stage preparing to dock with the Command Module