Tracing wiring runs in boats can be a painful task. Wire is often run in concealed areas, and at the ends, where it is visible, it’s usually bundled with a bunch of other wires. The good news is that most boatbuilders use the American Boat and Yacht Council color codes for boat wiring. Specific colors are used for specific equipment. Knowing these colors makes troubleshooting electrical systems easier.


Black Ground Negative / Neutral Main Return
Blue-Stripe Tilt up and or trim out Tilt and or trim circuits
Brown Alternator Charge Light Generator Terminal or Alternator Auxiliary Terminal to Regulator
Generator Armature Generator Armature to Regulator
Pumps Circuit Breaker or Switch to Pumps
Brown w/Yellow Bilge Blowers Circuit Breaker or Switch to Blower
Dark Blue Cabin & Instrument Circuit Breaker or Switch to Lights
Green or Green w/Yellow Stripe Bonding System Grounding Wires (if insulated)
Green Stripe Tilt down and/or trim in Tilt and or trim circuits
Grey Navigation Lights Circuit Breaker or Switch to Lights
Tachometer Tachometer Sender to Gauge
Lt. Blue Oil Pressure Oil Pressure Sender to Gauge
Orange Accessory Feed Ammeter to Alternator or Generator
Common Feed Distribution Panel to Accessory Switch
Feed Accessory Circuit Breakers or Switches
Pink Fuel Gauge Fuel Gauge Sender to Gauge
Purple Ignition Ignition Switch to Coil & Electrical Instrument
Instrument Feed Distribution Panel Electrical Instruments
Red Instrument Feed Distribution Panel to Electrical Instruments
Power Feeds Positive Main Power (particularly un-fused)
Tan Water temperature Water temperature sender to gauge
Yellow Generator Field Generator to Regulator Field Terminal
Ground Negative / Neutral Main Return
Yellow w/Red Starting Circuit Starting Switch to Solenoid


Wire / Conductor Sizes

Length (feet): Determined by measuring the length of the wire from the positive (+) power source connection to the electrical device and back to the negative (-) power source connection.  Note that the power source connection may be the battery, panel-board or switchboard.

Current (amps): Determined by adding the total amps on a circuit.

Wire sizes not covered in Table C or Table D may be calculated by using the following formula:

After calculating the Circular Mil Area (CM), use Table B to determine the proper conductor size.  The National Fire Protection Agency and Coast Guard require that the next larger conductor be used when the calculated CM area falls between two conductor sizes.

CM=K x l x L / E

CM = Circular Mil area of Conductors

K = 10.75 (Constant representing the mil-foot resistance of copper)

I = Current – amps

L = Length – feet

E = Voltage drop at load (in volts)

For Example…

Q.  A bilge pump draws 10 amps.  The positive run is 11 feet from the power panel, including the float switch.  The negative run is only 10 feet.  What size wire?

A.  Use the following formula to reach the correct answer:

CM = 10.75 x 10 (amps) x 21 (total length of run) / 0.36 (3% of 12v) = 6,271

The table below shows that 12 AWG wire has a CM area of 6,500 and is the correct choice. However, SAE wire has a CM area of only 5,833.  Under NFPA and USCG regulations, 10 SAE wire must be used.

CM = 10.75 x 10 (amps) x 21 (total length of run) / 0.96 (3% of 32v) = 2,352

Ampacity is the ultimate safe current carrying capacity of the wire before damage occurs to the insulation, without regard to voltage drop.  Because the insulation of most SAE wire types is not the same as ANCOR, this chart should not be used for other conductor types.  Use Table C & D to find proper wire size to insure adequate performance.

AWG Sq. mm AWG CM area SAE CM Area Ampacity Engine Space
Outside Inside
18 0.8 1,600 1,537 20 17
16 1 2,600 2,336 25 21
14 2 4,100 3,702 35 30
12 3 6,500 5,833 45 38
10 5 10,500 9,343 60 51
8 8 16,800 14,810 80 68
6 13 26,600 24,538 120 102
4 19 42,000 37,360 160 130
2 32 66,500 62,450 210 178
1 40 83,690 77,790 245 208
1/0 50 105,600 98,980 285 242
2/0 62 133,100 125,100 330 280
3/0 81 167,800 158,600 385 327
4/0 103 211,600 205,500 445 378