If you take out all the bulbs in that section you can test continuity from tab to tab. If you get it then one of the sockets is shorted to itself.

If that doesn't happen test each tab to ground. If you have continuity there then one of the tabs is shorted to ground.

Once you find there is a short you can go halfway down the chain and unsolder the lugs and test both side. Keep doing this until you have it isolated to a socket.

Usually somewhere in this process it jumps out

where the wires are soldered to the socket

you've got a short in a socket (or somewhere else) you need to follow the steps above to isolate it

yes, while the bulbs are out