now I am going to try to give u some ideas but i dont have my Tundra to check this for u..

For one - the load of the WOLO harn may be alot greater than the stock horn due to it taking much more current. Schematic says 20amps fuse so i am sure it draws at least 16amps.
Now the stock Horn i am sure is for 12vdc and draws less current. Seems u should of followed the one wire installation. Your photo shows the wiring is ok at end with ground lead to WOLO to Chassis but i think u blew a fuse when u reversed the wires and that puts the 12v to gnd and pop goes the fuse. I would of wired the external relay in line with the stock horn wire. this would put less stress on the tundra's relay which i dont know if it could or cannot take the higher current.

the hummiing noise -- not sure... only thing i would guess is maybe u fried the horn relay if fuse didn;t protect it.

If you put a voltmeter on the horn lead + , do you get 12V when you press the horn on the steering wheel - if u dont then its fuse. if u do get the 12V then attach to the WOA and if the 12V drops , the circuit cannot handle the current and fuse will blow...

hope this helps.

hope this helps somewhat and didnt confuse u. i dont know ure level of electrical..

The huming noise may be the stuck relay coil for the horn circuit...