Project Viper GTS: Part 5 – Radiator Fan & Wiring Upgrade

,Factory Fan Wiring Schematic

This is the Factory Viper Fan Wiring Schematic. The ECU sends a signal at 207*F to the first relay which turns the fan ON and OFF.  The second relay remains in the 87a position (Low Speed Fan) until the ECU sends an additional signal at 216*F which switches the second relay to the 87 position (High Speed Fan). This connection draws the most current and is the path that runs hot, overheats, and melts the relays in the previous picture.

NoSparc Fan Wiring Schematic

Above is our Modified Wiring Schematic.  The factory wiring is untouched to retain the ECU’s control of when to turn the fan on and off.  When power is sent through the factory wires, we use these inputs as signals to trigger our standalone relays which carry the load through dedicated power and ground wires so there is virtually no load going through the factory wires, this eliminates the possibility of melting them.

We used MIL-spec wire for the dedicated power and ground wires, which is routed through a 60 Amp circuit breaker then to the standalone relays to power the fan. To prolong the life of our standalone relays we used a pair of NOsparc® spark suppressors.  This setup becomes a plug and play installation by using the factory plug and only requiring an additional 2-wire plug to connect the new shroud-mounted setup.

Circuit Breaker

The first component is a 60 Amp Circuit Breaker (Part # CB3-SM-60 from Terminal Supply Co.) with a 42V Direct Current Maximum.

Relay Box

Next we needed to mount a pair of relays with this pre-wired harness and mounting bracket (Part # PT-B0S-12BK from Terminal Supply Co.).  They are individual and slide lock together to form a single mounting block.

Relays 50A

We sourced a pair of 50 Amp TE Relays rated to 100*C (Part # RLY-C-X032 from the Electrical Depot) to carry the load of the new 40 Amp fan.


  1. Radiator fan wiring upgrade they auxiliary relays what wires output to the fan either number or color it’s not clear thank you for your help

  2. Have a customer with a 96 wanting to do this upgrade to his cooling system, any idea where the cooling fan may be available?

  3. That’s weird. I’ve always been taught to crimp ring terminals on the cut side, so it forms a B-type crimp that secures the wire. Well, whatever works!

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