is the fuse in the clips tightly? Try wiggling the fuse.

if nothing, grab your voltmeter and measure the AC voltage. One probe goes on the BLK-WH wire that is attached to almost all the lamps, the other probe poke the wires on both ends of the 10A fuse with the WH and WH-RED.

if you can tell which wire is BLK-WH on the transformer, you can put the probe there. There's also a WH-BL wire on the transformer ... you don't want to be on that one (it won't hurt anything, you just won't get a sensible reading).

got 6VAC on both ends of the fuse? If yes, poke the switch blades on the T relay (WH-RED and WH-BLK wires) and see what you have.

the typical problems are:

1] broken fuse filament at the cap where you can't see it
2] poor fuse clip tension. Remove fuse and bend in the clip ears to clamp the fuse harder. If the clip breaks, it was no good anyway.
3] corroded/oxidized fuse clips
4] T relay switch no good (6V on WH-RED, much lower on WH-BLK)
5] poor plug connections - will show up as low voltage on the plug or socket, but not both
6] broken wire - BLK-WH could be broken or the WH-RED/WH-BLK side of the circuit
7] short pulling the voltage way down