marine wiring proceduresmarine electrical color codes

Proper marine wiring practices are difficult to come by these days, so I have put together a short informational packet on how to properly tackle a wiring project on your boat.

Most importantly, you should always follow the color-coding standard used in the industry when adding or replacing the wiring in your boat.

The 12volt standard is as follows:

  • Black - Common ground for the electrical system
  • Red - Main (+) for the electrical system
  • Purple - Accessories positive lead between key switch and positive lead of accessory
  • Purple w/white stripe - Positive lead between key switch and choke solenoid on engine
  • Yellow w/red stripe - Positive lead between key switch and starter solenoid
  • Red w/white stripe - Positive lead feeding power to individual solenoids on an engine
  • Brown - Positive lead for pumps like bilge or wash down
  • Tan - Sender lead for temperature gauge
  • Pink - Sender lead for fuel sender in fuel tank
  • Dark Blue - Lighting - primarily in instrument panel gauges
  • Gray - Navigation lights
  • Light Blue - Oil pressure sender lead between engine oil pressure sender and gauge "S" terminal
  • Orange - Alternator output lead which connects to starter solenoid positive post to recharge batteries
  • Yellow - This color in a solid form is seldom used but can be used for windshield wiper circuits
  • Green - Vessel earth ground which is used in bonding circuits to provide an earth ground to the vessel
  • Orange w/yellow stripe - Horn positive lead
  • Purple w/red stripe - Blower positive lead as well as accessories such as nav equipment and radios
  • Tan w/ stripe - Warning circuit between sender and alarm circuit, match stripe color to sender type, ie blue for oil, brown for temp etc

With the use of proper color-coding, your service tech will be able to quickly solve wiring problems. Next we will look at what kind of wire to use. I always use tinned stranded electrical wire because it resists corrosion far better than any other wire. Your wire must have an insulation temp rating of at least 105 degrees C to be coast guard approved. Never use wiring not designed for marine use. For connections, there are several options. Solder and heat shrink is the best, followed by crimped terminals which use an epoxy sealer in the heat shrink tube which is part of the terminal, and lastly, the standard insulated crimp terminal.

As a good practice, you should always use shielded power cables for connecting electronic equipment. The use of shielded cables will reduce electrical interference and allow you to get the best reception.

Wire size is as important as everything else. Always use the proper size wire for the electrical load it will be carrying. If you have a 10 amp circuit less than 20 feet in length, use 14 gauge wire. Use 12 gauge if it is less than 30 feet. For circuits which are relatively short use a wire gauge one size larger than the size wire the accessory you are connecting provides.

Always provide fuse protection for your circuits, including the main feed from the battery to the fuse panel and keep it as close to the source as possible.

If you have a specific question regarding a project you are working on, feel free to contact us anytime. We are always happy to assist our customers.

Lately we have had a lot of you looking for information on marine wiring. For instruments, always maintain seperation from your boats auxilliary systems. All guages are to be wired into the engine harness and power supply. Use the ground wire (black) from the key switch end of your engine harness for the ground terminals on your guages. Use the purple accessory lead for your ignition terminals and the individual sender leads for the sender terminals. Connect fuel senders sererately and with a direct battery ground lead. To test a guage and sender for proper function, with power to guage on, ground the sender terminal of the individual sender to a known ground, this will cause the guage to move to it's full position. If it does not move, the guage is bad, if it does move when grounded but not in normal operation, then the sender is defective.

If you have a specific question you need answered, feel free to email it to us at and we will be happy to reply with an answer.

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