I did this:
That's a 6 position fuse block and the arrow points to a 40 amp rated
RELAY here
The 12volt coil of the relay is wired to the work light plug located under the left fender in my L3800. The circuit is energized whenever the key is 'on'. The only current drawn from that work light circuit is to power the relay coil.
I ran a 12/2 wire pair from the battery (fused at 20amp at the battery) to the relay. The + side is switched by the relay contacts to power the fuse block.
From the fuse block you can then run up to 6 circuits in the rear of the tractor. I have several in use now - forward and rearward switched led work lights, a connector for my snow blower chute rotation and another for the chute deflector. I converted them from manual to electric control.