The voltmeter you have purchased is designed for easy installation on an INJOY style lure machine (See Below).   If the components of your lure machine are arranged differently, you may need to mount the voltmeter in a different location from that shown below.

To install the voltmeter on your lure machine, you need to locate and mount the unit (using the screws provided) so that it is easily seen while operating the lure machine.   Next, connect the red wire to the 5/16" (large) terminal located on the right side of the solenoid.   If your lure machine has a different style solenoid than shown above, the red wire needs to be connected to the same terminal as the positive cable connected to the battery.  The black wire can be connected to any grounding fastener but the solenoid mounting bolt is convenient and recommended.

The voltmeter will constantly monitor the voltage of the battery connected to your lure machine.  A fully charged 12 volt battery in good condition will register between 13 and 14 volts.  These voltmeters are not a precision instrument but they allow a relative reading of the battery condition at a glance.  It is a good idea to index your voltmeter by attaching it to a fully charged battery and comparing the reading with that given by a hand held precision voltmeter (if you have one).   If you do not have access to a precision voltmeter, than just notice what the reading of the voltmeter is with a fully charged battery...it should be reading close to the 13 volt point.

Keeping an eye on the voltmeter throughout the day will give you valuable information as to what is the condition of your battery and the battery charger, if you are charging your battery in place.  If both items are doing their job or adequate for the job at hand, the voltmeter should return to the 13 volt reading between courses (time wise within 5 to 10 minutes).

A normal situation would be as follows: after running a course, the volt meter reads 12 or 11-1/2 volts and the battery charger should bring the battery back to 13 volts in 5 or so minutes.   If after each course the volt meter shows a lower reading than before that course, the battery or the charger is not doing the job at hand.

When the battery drops below 11 volts it is time to exchange the battery for a new fully charged one or recharge the battery now attached to the lure machine.