2-Speed 70A Dual Fan Relay Kit – EFI Applications, Negative Trigger


Our 2-Speed 70A Dual Fan Relay Kit has been designed for EFI applications with a pair of traditional two-wire single speed fans.  This greatly reduces operating current, in-rush current, and fan noise.  Powers fans requiring up to 35A continuously with minimal voltage drop!

This completely waterproof kit installs easily and plugs directly into your electric fans.  Kits are offered with either traditional fan connectors or Metri-Pack 630 series fan connectors.

Includes full color step-by-step instructions and all hardware shown.

Full specifications outlined below.




Compatible with EFI Applications where the ECU has two fan activation outputs, both negatively triggered, and each must be programmable for different temperature set points!


Triggering is fully automatic (see below for specifics).

Fans come on in Low Speed via the ECU’s Fan 1 Output – which should be set to activate at 165 degF or so.  Fans shift to High Speed via the ECU’s Fan 2 Output – which should be set to activate at 185 degF or so.

Low Speed – Two fans operating in Low Speed consume less than half of the current required of a single fan operating at full speed.

High Speed – Inrush current to the fans is reduced to approximately 50% of what a pair of fans require when switching ON from a dead stop.


  • Fully automatic via low current fan outputs from EFI ECU
  • Compatible with ECUs outputting a Negative (-) trigger for the fan circuits
  • A/C triggering is accomplished by interfacing the A/C compressor with the ECU’s A/C input – when the A/C is turned on, the idle is raised and at least one of the fan outputs will be activated

Harness Specifics

  • Wiring to Battery: Dual 10 AWG TXL, terminated with a 5/16″ eyelet
  • Wiring to Fans: Dual 10 AWG TXL pairs, terminated with traditional fan connectors or Metri-Pack 630 connectors – your choice
  • Harnesses dressed in Split Braided Tubing for that show car look!Harness Lengths:
    • Power Harness to Battery:  3ft
    • Output Harness to Fans:  3ft (Metri-Pack 630 harnesses are 1ft longer)
    • Trigger Inputs from ECU:  2ft
    • Switched Power Harness:  6ft


Maximum Current Capability: 35A per fan for a total of 70A
Typical Voltage Drop through wiring when driving a pair of 16″ fans requiring 24A continuous each with 13.8 VDC of input:

  • Immediately after power up: 340mV or 2.5%
  • After 30 minutes of continuous operation: 390mV or 2.8%
  • After 5 hours of continuous operation:  400mV or 2.9%

Dimensions of Relay Module with mounting bracket installed: 62mm wide x 59 mm deep x 94mm to top of mounting bracket


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