How to install voltmeter

Just bought this tiny LED voltmeter from ebay, now just wondering where is the best point to tap in the source. can i just connect the black cable to the chassis ground and red wire to the main headlight positive? i'm not that good when it comes to electrical stuff.

Inside the headlight there are 2 accessory plugs marked ACC1 and ACC2. one is always on and the other one is on after you turn the key.
Just plug it in on the one after the key. Easy!