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

Fan wired

Having connected MIL-spec wire to all six wires (three on the fan and three on the plug) we shrunk everything in 3/8” Raychem shrink wrap and used adhesive shrink to seal off the ends.  We ran both sets of wires to the passenger side where our relays are mounted and zip tied the wires neatly out of the way.

Despite using standard (cheap) automotive-grade wire with relatively weak insulation, the 99+ fan has a decent gauge wire given its 40 Amp draw:

Chassis Side Wire ColorFan Side Wire ColorDescriptionGauge Wire
BlackBlackGround12 awg
Dark Green (middle)Brown/Red (middle)Low Speed Fan14 awg
Light GreenBrownHigh Speed Fan12 awg

NOsparc Wired

The NOsparc® arc suppressors are wired as drawn in the diagram earlier.  The Red wire connects to the hot side which always has power while the Black wire becomes hot once the relay triggers it to switch on.  This is when the Arc Suppressor does its job to eliminate arcing to prolong the life of the relay.

NOsparc Gap

The NOsparc suppressors are also mounted with a ¼” gap for better insulation.

Relay Wiring

Wiring the power, ground, triggers, and NOsparc was a bit time consuming given that each wire was crimped, soldered, and shrunk.  This was as elegant as we could make it.

Finished Wiring

Now the wiring is finished.  The main power and ground from the circuit breaker travels along the bottom of the radiator shroud and up to the relays before following the new wires to the center of the fan motor. The factory plug’s ground and low/high fan wires travel to the relays across the radiator face and act as triggers to send the power to the fan motor via 10 gauge MIL-spec wire.


  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!

  4. good evening i have a 1999 viper GTS and i just got the radietor from you do u by any chance sale the hole kit for the fan to make it work better please let me know so i can buy ti thanks

    1. What temp does the fan kick on? Did you change the low or high speed fan temp threshold by flashing your ECU? If you’re tripping the 60A circuit breaker, then you need to troubleshoot and find what is causing the excessive amp draw.

  5. Is the Bosch relay with the 332 209 151 number the same relay? Stats look similar to the one you have installed

    1. Those appear to be 30A relays vs the 50A relay that I used. I would recommend using the part number for the 50A relay.

  6. can u send me more detail about the wires evething look nice but i can not see every cable where they go to make shure i conected right i need the order or a better pictures can u send me a diagram i got all the parts thanks

Leave a Reply

Your email address will not be published. Required fields are marked *