How do I test for leaking current in my boat’s electrical system?

First, turn off all electrical equipment and fixtures aboard, then disconnect the positive connector from the boats’ battery terminal and connect the positive lead of the multi-meter to the battery post and the negative lead to the connector.  Starting at the 10 ampere (or highest current) range of the meter, check to see that there is no current flow, then switch to the low current ranges. With the perfect boat wiring and equipment, no current should flow at any setting.  A normally ‘clean’ electrical system will have a leakage current of less than 1 milliampere (0.001 amp).  Leakage of a few milliamperes indicates a small amount of corrosion – hardly dangerous – but something to locate and correct.  However, if the meter shows a sizable fraction of an ampere, separate circuits should be switched off one at a time to find which is at fault, and the wire or equipment repaired or replaced promptly.  If leaking of this magnitude is found, leave the battery disconnected until the trouble is cured.