Join Date: Aug 2009
Location: Washington, the state
Keep in mind that the purpose of a fuse or circuit breaker is to protect the wire from excessive current which causes overheating. The capacity of the fuse depends on the ampacity of the wire, and sometimes on the device you're powering. As GW says, first decide on what you'll plug into the cig lighter sockets, buy sockets that will more than handle the load, then wire that more than handles it, and suitable fuses. Loads like GPS, cell phone charger, etc. are miniscule. Heated gear is higher. Aftermarket horn is high. Some lights are high load. Check the label on an air compressor.
Sometimes the load is listed in watts rather than amps. Watts are the unit of electrical power. Amps are the rate of flow of the electrons. Voltage is the force of the electricity.
Watts = volts x amps
Amps = watts ÷ volts; for example 120 watts on a 12 volt system draws 10 amps, so you'd want a circuit with at least 12 amp capability (20% excess rule).
You want the voltmeter on a switched circuit, i. e., a circuit that is on only when the key is turned on. The voltmeter uses a very small amount of power, and eventually it could draw down your battery.
"Older people who are reasonable, good-tempered, and gracious will bear aging well. Those who are mean-spirited and irritable will be unhappy at every period of their lives.
"Let each of use properly whatever strengths he has and strive to use them well. If he does this, he will never find himself lacking."
Marcus Tullius Cicero
Last edited by PTRider; 02-21-2014 at 04:00 PM.