what is the
mod out of curiosity? maybe you could just mount the meter in the
mod? add a switch if you don't want the meter on all the time?
otherwise simply make a parallel lead from center post to center post and outer to outer then test your mod for polarity most are center positive...beyond that wiring the meter is simple pos to the pos lead and neg to the negative... if you need a better description I need to know what you are enclosing the meter in and what model is the meter...