Bosch Style Relay Boxes SPDT – N.O./N.C.

(14 customer reviews)

$165.00$275.00 (USD)

MGI’s Bosch-style relay box is designed for advanced high-power wiring projects requiring both Normally Open (N.O.) and Normally Closed (N.C.) circuitry. Can handle up to 24A resistive loads @ 12vDC, and up to 12A electric motor loads (fans and pumps).

  • Pre-wired with 4, 6, or 8 SPDT Bosch-style relays rated 40A
  • Built-in smart LED fuses that glow when blown
  • Comes with main feeder and main fuse
  • Relay corresponding LEDs
  • 1 x N.C. output available
Clear All
    Reset options

    Choose your own fuse and feeder cable sizes.


    Protect your relays from flyback voltage when the power supply is suddenly disconnected. See What is a Flyback Diode? for more info.

    All relay panels are factory wired with #14 AWG. Click the checkbox below if you wish to have one or more relays installed with #12 AWG wire instead.

    Dust-tight and weatherproof IP66 rating. See our RCP enclosure page for more details.

BULK ORDERS – please contact for availability.


Reliable High-Power Control
for when regular switches won’t work


Your high-power solution. When regular switches can’t handle high-current loads, adding relays can become a complicated and messy project. That’s where MGI steps in ⁠— our fused relay boxes provide centralized control and protection with minimal wiring involved.


Wiring is made easy. Each bosch-style relay box comes with a red main feeder cable and labeled screw terminals. Use the Installation Manual and wiring diagrams to help connect your power source, switches, and loads. It’s that easy.


Quality is Guaranteed. Our relay boxes are routinely tested, with relays rated 40A at 12 volts to ensure optimal reliability come race time. Produced only with GXL high temperature wire, with no-nonsense screw terminal strips for reliable input and output wiring.

Bosch Style Relay Box Features
use our interactive builder to customize your multi relay control box

Choose the Number of Relays

We understand that space is a valuable commodity in your rebuild or showcar. That’s why we’ve designed automotive relay boxes with your choice of 4, 6, or 8 relays. Each relay box has at least one 5-pin relay that can be wired for normally closed operation if needed.

MGI relay panels can also come with flyback diodes installed. The use of a diode in a relay circuit prevents voltage spikes from arising when the power supply is disconnected.

Choose Your Fuses

Each MGI relay box comes with fuses tailored to your specific loads. Don’t know what fuse sizes you need? Don’t worry — MGI uses an industry standard, tried-and-true formula to provide recommended fuses sizes for your individual loads. A similar approach is used to calculate the main fuse size.

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

With this information, MGI will supply you with appropriate fuses unless otherwise selected.

Number of Relays
Main Fuse
Feeder Cable

Relay Box Wiring Diagrams
how to install 4, 6, and 8 relay boxes


Battery Power

relay box power

Connect the red main feeder conductor to the car starter’s battery power terminal. Then, install the supplied main fuse and holder in the main feeder conductor between the starter and the power stud found inside the panel.


Switches & Grounds

relay switches

Connect the black ground wire (with red ring terminal) to the auto chassis. Then, connect the control circuit wire(s) to your switch inputs, with outputs connected to the appropriate screw terminals.


Outgoing loads

relay box wiring

Connect your loads to the appropriate screw terminals. Ground your loads. See the 4, 6, and 8 relay box diagrams above. In addition to regular N.O. circuits for each relay, each RCP has 1 optional N.C. circuit.

what comes with every SPDT Bosch style relay panel kit

  • Aluminum frame and your choice of 4, 6, or 8 built-in relays
    • 40 Amp SPDT relays
    • Optional N.C. circuits
  • Relay-corresponding LEDs for visual troubleshooting
    • When relay closes, LED turns on
  • Integrated LED blade fuses (+ spares)
    • ATC / ATO style blade fuse with LED light that glows when blown
    • Available in sizes 5 to 40A
  • 5A LED control circuit fuse (+ spare)
  • Main fuse & fuse holder
    • Mini ANL bolt-down fuse
    • Available in sizes up to 150A
  • 5′ main feeder conductor
    • Available in sizes up to #2 AWG
  • ½” strain relief cable gland connector(s)

Answers to Popular questions

Why buy a fuse & relay box?

When rebuilding, restoring, or refurbishing your vehicle, you’re bound to need electric pumps, fans, spotlights and more. These high-current devices will damage regular ignition key switches or low-current switch panels — however, an electromagnetic switching relay box will give you the safe and reliable control you need.

Can this relay box operate “normally closed” devices?

Yes! Our unique SPDT Bosch style relay boxes can power devices that are normally closed.

  • RCP4 has one N.C. output (terminal #17)
  • RCP6 has one N.C. output (terminals #20)
  • RCP8 has one N.C. output (terminal #26)
It’s as easy as connecting your loads to the appropriate N.O. or N.C. circuit screw terminals. See the wiring diagrams for more information.

some popular relay panel projects

Nitrous Trans-Brake Circuit

A nitrous trans-brake system is a great example of SPDT wiring that uses both the N.C. and N.O. relay box circuits.


Relay Panel Specs
without feeder, fuse, and fuse holder

Physical Dimensions (L x W x H)
5.00" x 3.38" x 5.25"
22.0 oz

4 Relay Control Panel — RCP4

Physical Dimensions (L x W x H)
5.00" x 3.38" x 6.50"
29.0 oz

6 Relay Control Panel — RCP6

Physical Dimensions (L x W x H)
6.13" x 3.38" x 7.75"
38.0 oz

8 Relay Control Panel — RCP8

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

14 reviews for Bosch Style Relay Boxes SPDT – N.O./N.C.

  1. Raym (store manager)

    high quality and works well. Not cheap plastic like other relay boxes.

  2. Dan_H (store manager)

    Good but wish it came with a waterproof box for my buggy in the mud.

    Uploaded image(s):

    Image #1 from Dan_H
  3. Anonymous (verified owner)

    Very high quality! Definitely recommend

  4. Robert (verified owner)

    Quality was excellent very well made

  5. Greg Brannon (verified owner)

    We are converting our 65 Nova race car from carburetor to electronic fuel injection. The wiring needed to be redone along with incorporating relays. Your six relay Bosch style box fit our needs exactly and when we received it we were very pleased with the quality and ease of installation.

  6. Andrew F. (verified owner)

    Very nice product. I bought two panels and they were very well made. Two panels going into my street race car.

  7. Frank B. (verified owner)

  8. Chris D. (verified owner)


    Uploaded image(s):

    Image #1 from Chris D.
    Image #2 from Chris D.
  9. James Fink (verified owner)

  10. James Hembree (verified owner)

    The light up fuses are a decent idea but the don’t fit the slot correctly. Nothing a standard fuse won’t fix but definitely not correct

  11. Johnny Rushing (verified owner)

  12. Tim Takash (verified owner)

  13. Kevin Stafford (verified owner)

    I’m not all the way finished yet but everything I received looks great and the help I received over the phone was more than great

  14. Paul K (verified owner)

    Same comments as above.

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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.