Use the plastic tray space behind the computer to velcro the relay down if you don't want to drill holes to mount it.
Run a 20 - 25A cable from your battery via the fuse to terminal 30, and run another from 87 to the positive of your grips. The grips negative can be earthed anywhere on the frame. Use corrugated cable tube to protect the cable from rubbing and heat. Use good quality terminals and it pays to use heat shrink over them and any joins if you can.
Don't hook the grips to your battery or directly to any other feed on the bike. You WILL end up with a flat battery, and you may burn your wiring if you don't use a relay.
On the bandit I ran the "brain" of the grips behind the fuse box and indicator relay under the left side cover. It cable ties onto the metal frame that holds them both and bolts to the bike.