Hey Anthony,
I could be wrong, but I don’t think that was ever a default key binding to switch windows. To switch windows you can:
Move to the next window: <prefix>: n
Move to a specific window number: <prefix>: <win #>
To set <prefix>: l as your next window command you could do:
bind key l next-window
Before any of that, you’re not confusing windows with panes are you?