Underwater Boat Light Wiring Done Right

Power distribution boxes keep underwater boat light wiring orderly and trouble-free while giving you a way to control your lights.

The SCM-PD+ is a power distribution box for underwater boat lights and underwater yacht lights. This watertight box powers and controls up to six single-color, two-color, or color-changing underwater lights.

Who Needs the SCM-PD+?

Some boats need more than four underwater lights. Yachts, boats with a wide beam, and boats with multiple outboards often need five or six lights to get even coverage across their transom.

But wiring that many underwater lights together is time-consuming and expensive. It leaves a complex jumble of wires that can lead to ongoing problems down the road.

And then, of course, you need a way to control your lights.

Power distribution box for underwater boat light wiring.
The SCM-PD+ keeps underwater boat light wiring neat, dry, and secure.

How It Works

One of the biggest advantages of the SCM-PD+ is how organized, secure, and short it keeps your underwater boat light wiring. Short wire runs have less voltage drop. You use less wire and smaller gauge wire.

First, mount the SCM-PD+ in a dry location under the deck, high in the bilge, or in a console. Select a spot that is within easy reach of both the light cables and a power source.

Next, rout wire cables from each light to the power distribution box. The cables stay short and secure with little to no voltage drop. Each light gets its own cable gland, set of connectors and fuse.

The cable enters the box through a cable gland that holds it in place and seals out moisture. Then, wires from the cable snap into color-coded connectors that match the wire colors. This makes wiring your lights fast and easy with almost no chance of wiring them wrong.

After that, a positive wire connects the box to a power source through a fuse or breaker. Then, a negative wire connects the box to a negative bus bar.

Finally, the power distribution box connects to a set of low power wires from a switch. The switch is how you communicate with your lights.

How to Control Underwater Lights

All Shadow-Caster underwater lights can be controlled in one way or another.

  • Single-color lights can fade, strobe, or chase from one light to the next.
  • Two-color lights change colors plus fade, strobe, and chase.
  • The SCM-CC will change between blue, white, red, and green. It also fades between blue and white or fades between all four colors.
  • The SCR-CC can change between 13 pre-set colors. It will fade between blue and white or fade between all colors.


To control underwater lights you need a way to “talk” to them. Shadow-Caster developed Shadow-Net technology to do just that.

Shadow-Net is a communication protocol that allows the SCM-PD+ to send commands to the lights. The SCM-PD+ does this with a momentary rocker switch.

  • Flip the switch ON and the lights come on.
  • Pressing and releasing the momentary switch to change colors.
  • Holding the switch down for two seconds to set fade, strobe, and chase mode.

Light Controlers

Shadow-Caster makes two light controllers that work with the SCM-PD+. Using a light controller gives greater control over underwater lights.

SCM-PD-Plus Color Changing Power Box


First is the SCM-PD-Combo. It is an SCM-PD+ power distribution box with built-in wireless control. A two-button Key FOB is used to remotely control the underwater lights.

The remote Key FOB gives more control over your lights. Use it to change colors, fade, flash, and chase the lights, you can set how fast the lights cycle through each mode.

4 zone led light controller


Next is the SCM-ZC four-zone light controller. This controller separates the lights on your boat into four zones. One of those being your underwater lights.

The SCM-ZC gives you greater control over your underwater lights.

  • Sync your underwater lights with the other zones or control them separately.
  • Change the color and hue of your underwater lights.
  • Dim your lights.
  • Fade and strobe a single color or multi-colors.
  • Sync your lights with music.
underwater boat light wiring customizations
1) Channel Power Switches
2) Light Function Switches

Customize Your Light Setup

Customize the SCM-PD+ to match whatever and however many lights you have. It doesn’t matter if they are single-color lights, color-changing lights, or a mixture of both. The SCM-PD+ will get the most out of the lights you have.

Switch on Your Channels

To start, the SCM-PD+ has six channels. One for each light. Each channel has a switch to turn it ON or OFF.

Set a switch to ON to turn the power ON for that channel, off to turn the power off. Channels 1-4 are set to ON at the factory. When using channels 5 and 6 be sure to turn them on before installation.

Set How Your Lights Function

A set of three switches control how your lights function.

Switch 1 enables Shadow-Net. It is set to ON at the factory and should not need to be changed. Only turn this OFF if you don’t want to change colors, fade, flash, and strobe your lights.

Switch 2 enables Chase Mode. This switch is set to OFF at the factory. Chase Mode briefly turns the light in position 1 ON, turns it OFF and turns the light in position 2 On, and so on through all lights before starting over again. If you want your light to chase, set this switch to ON.

Switch 3 enables Extended Colors. This switch is set to Standard Color Range at the factory. The extended Color range is used with the SCR-CC, RGB color-changing lights. It extends the pre-set color range from 4 to 12. When using SCM-CC four-color lights, the color range should be set to Standard Colors.

Making Underwater Boat Light Wiring Easier

If you are installing five or six underwater boat lights you need the SCM-PD+.

  1. First, it makes wiring underwater lights much easier. Your wiring stays uncluttered and you save on installation costs.
  2. Next, It protects your lights from the harmful effects of moisture. Wiring connections stay dry and trouble-free.
  3. Finally, it gives you control over your underwater lights. Change the color of color-changing lights or fade, strobe, and chase single color lights.

To order, go to the SCM-PD+ product page.
Click on the green button to Go to Secure Checkout. That will add the SCM-PD+ to your shopping cart.

After that, you can add your favorite underwater lights and checkout through PayPal.

The alternative to the SCM-PD+ is the SCM-PD-Relay-4. It is a power distribution box for up to four underwater lights. It gives you all of the same features as the SCM-PD+ at a lower price.

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