From your photo i can clearly see the latch to lock the swing arm closed, but I'm still not seeing a lock, to lock the swing arm in the open position.
Below are a few photos of a swing away tire carrier mounted next to a Land Cruiser pintle hitch, in these photos you can clearly see the quick pin lock that is used to lock the swing arm in the open position.
This lock setup can lock the swing arm in 2 positions, 110 degrees and 180 degrees.
Take note of another item included on this design, due to the weight of the swing arm with the tire in place this mount has a positive stop bracket welded in place. This stop will prevent the swing arm from being able to swing all the way around, and possibly damage the trucks body.
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