Relay Bank & Harness Kit

(2 customer reviews)

$40.00$70.00 (USD)

An MGI automotive relay harness set has proven to be a cost-effective, compact, and reliable solution for powering high-current electrical devices.

  • Control automotive & marine 12v electrical accessories such as fans, pumps, and spotlights
  • Reliable 12 volt 40 amp SPDT switching relays
  • Easy-to-reset push button breakers
  • High-temperature wire for all inputs and outputs
  • Compact design allows for convenient placement
Clear All
    Reset options

    Choose your breaker sizes.

BULK ORDERS – please contact for availability.


High-Power Relay Control
what makes a relay bank & harness kit special


40 amp SPDT relays are a reliable solution to high-power accessory control. Easy-to-use socket bases are pre-wired with high-temperature GXL and premium stranded copper — install the relays with ease and confidence.


Rearrange, separate, and combine. an MGI relay harness is versatile, which makes it an ideal solution for cars, trucks, boats and more. Add or substract any number of relay bases with ease. SPDT relays with both a normally open (N.O.) and normally closed (N.C.) output gives you greater control of your accessories.


Choose the number of relays and their corresponding breaker sizes using our interactive builder. It’s that simple. You’ll be powering your 12v accessories in no time.

Relay Harness Features
use our interactive builder to customize your automotive relay harness

Choose the Number of Relays

We know that space is valuable in your car, truck, boat or off-road vehicle. That’s why we’ve designed power control harness sets with your choice of 3 to 6 relays, each rated 40A at 12 volts. It’s that simple.

Unsure of how many relays you need? Our interlocking relay bases lets you add or subtract any number of relays with ease.

Choose Your Breakers

Each MGI relay bank comes with breakers tailored to your specific loads. Don’t know what breaker sizes you need? Don’t worry — MGI uses an industry standard, tried-and-true formula to provide recommended breaker sizes for your individual loads.

  1. Simply enter your current load into the calculator
  2. and indicate whether it is a motor load.

With this information, MGI will supply you with an appropriate breaker size unless otherwise selected.

Wiring Made Easy

Each relay harness comes with lots of wire for both inputs and outputs. After mounting the relay harness in your location of choice, use the relay socket diagram as a guide to wiring your power source and loads.

Number of Relays
Input & Output Wire

What’s included

  • 40/40A changeover relays
    • 5 Pin wiring with N.O. and N.C. outputs
    • Interlocking bases
  • Custom sized branch breakers
    • Your choice of breakers sized between 5 – 30A
    • Easy push button reset
  • 2’ of GXL #14 AWG colored wire for each breaker input
  • 5’ of GXL #14 AWG colored wire for each relay N.O. output
  • 5’ of GXL #18 AWG white wire for each relay coil positive
  • All necessary crimp terminals


RCS Specs
relays and base only

Physical Dimensions (L x W x H)
3.75" x 2.00" x 1.625"
7.3 oz

3 Relay Control Set — RCS3

Physical Dimensions (L x W x H)
5.00" x 2.00" x 1.625"
9.8 oz

4 Relay Control Set — RCS4

Physical Dimensions (L x W x H)
6.25" x 2.00" x 1.625"
12.2 oz

5 Relay Control Set — RCS5

Physical Dimensions (L x W x H)
7.38" x 2.00" x 1.625"
14.7 oz

6 Relay Control Set — RCS6

All dimensions and weights are supplied as general information only and are not certified.

2 reviews for Relay Bank & Harness Kit

  1. Jay H. (verified owner)

    I rewired the entire electrical system on my ’71 AMC Hornet. MGI was the primary source for all of my electrical hardware. Quality parts, fair prices, awesome tech support (Raymond and Marcel). I used a number of their components, including relays, to build a new electrical box in my glove box. So much easier than building everything from scratch…Highly recommended.

    Uploaded image(s):

    Image #1 from Jay H.
    Image #2 from Jay H.
  2. Jay H. (verified owner)

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Before finalizing your purchase

It is important to familiarize yourself with the MGI panel Installation Manual. Not only does this help you to select the appropriate options for your race panel, it will enable you to tackle any troubleshooting issues with confidence.