A-Most onboard systems such as chartplotters, fishfinders and multifunction displays often have built in volt meters. This will tell you that current is getting to the points they are installed. However if an instrument does not turn on and fuse is not blown, you will need a portable voltmeter. If no voltage is present on the instrument you are checking, test at every electrical connection between the instrument and the battery. When you find a spot that the reading is 12 volts, you have fond the spot with the bad connection. Most likely you will find a corroded or poor connection or a loose connection or a defective switch or breaker.
Q-How can I figure out the positive and negative leads before re-connecting my electrical equipment?
A- First of all, never leave your dock without a portable voltmeter. Before re-connecting your electrical equipment, place the leads of your voltmeter on what you think are the positive and negative 12V leads going to the power source. Observe the reading on the meter. If the reading is 12V, then you have the right polarities and you can safely connect your equipment. However, if the needle reads backwards, instead of moving to the right t moves to the left, or if the digital voltmeter reads -12V, then you have the polarities reversed and you will need to reverse them. Remember to never leave the dock without your voltmeter.
