Startup current for the Stebel measures at 15 amps. Use the relay. On touring models, the relay will drop right into the spare relay spot under the seat, that is for the siren on police units. You will need to lengthen the wires to reach the relay spot. You can also use the in-line fuse or modify the harness to put the fuse in the siren fuse slot in the fuse block. Soon I will take mine the rest of the way to a clean installation.
I use the Pro-Pad Mini-Beast, which is a repackaged Stebel. Pretty much plug and play, except for the short wires, keeping me from putting the relay in the under-seat slot. It has a nice sturdy mount, and a cover that resembles a smaller version of the air cleaner cover on the other side.
Enjoy,
Rich P