The 7 Best Practices For Wiring Automotive Fans With SPAL USA

We all know how important it is for a car to keep cool in the summer months because overheating can easily happen. But, engine cooling is something people can often forget during the cooler part of the year. This is interesting, considering all the winter projects going on in garages across America. So, now that you have your prized piece of American muscle tucked away like the majestic groundhog, take some time to prep it for cruising season.

Focusing specifically on a car’s cooling system, we worked with the experts at SPAL Automotive Technology to compile a list of the most common questions and issues they deal with on a daily basis when helping people beat the heat. Speaking with Greg Goeders and Brent Chuck from SPAL, we found out their best tips and tricks to reliably wire fans. Some of them might be “no-brainers,” and others you might have never thought of, but they’re all great tips.

So follow along, and don’t be intimidated by things like wiring, relays, and thermal switches. Remember, you’ve got a few months to figure it out, and with these tips, it should be a piece of cake.

Notice how each fan on our project has its own circuit. Two power, two ground, and two signal wires for the fan relays are all routed independently of one another. There are also two separate fuses under the black cover. Redundant? Maybe, but that’s what we’re after.

1) In This Case, It’s Okay To Be Redundant:

  • “Use one fuse and one relay per fan. Fusing each fan individually is critical, but having a dedicated relay/circuit will maximize applied voltage, which means more fan performance. When you have separate or redundant fan circuits, it’s less likely to leave you stranded/overheated on the side of the road, as it is likely to lose the function of both fans.”

Overloading one circuit with the high-amperage associated with fans is a recipe for disaster. To avoid burnt wires and fried fuses, take this tip and assign a fuse and relay to each fan if you are running multiple.

2) Pay Attention To Fan Loads And Splice Points:

  • “Pay attention to current loads of the fans. Splices and connectors are common points of failure. It’s important to use a splice that is sufficient for the current load of the fan.  Sealed splices are preferred.”

When you start to list all the things that can go wrong with your wiring, it seems like there’s a good reason to be wary. But, if you take your time and do things the right way, there really isn’t much to be afraid of. One of the things people seem to rush through and end up paying for later is their splices and connections. If ever there was a weak point in a wiring harness, it’s improper splicing and connecting, especially on something drawing as much power as a set of fans. Insecure connections are a common source of heat, and fire can follow – at the very least, a fried wire.

Solder and heat shrink your connections when you’re able to, and if you have to use butt connectors, make sure the connections are solid. And, for the love of all that is horsepower, don’t just use electrical tape (the equivalent of hopes and dreams) to hold your connections together!

With the cover off, you can see our two separate fuses for each circuit. Fuses are the preferred method to protect our wiring harness because, while they are terminable, they offer a greater level of protection.

3) Protection Level Critical:

  • “Circuit protection is critical. Fuses are our preferred method of circuit protection. Self-resetting circuit breakers may not adequately protect the harness in the event of a stall. Replacing a fuse with an equivalently rated circuit breaker does NOT offer the same level of protection.”

This is an interesting tip from the experts at SPAL because it isn’t one you’d think to be accurate, but it is! Aside from being much more cost-effective, fuses are considered to be a safer means of overcurrent protection when compared to a circuit breaker.

Supposedly, fuses are less prone to malfunction since there are no moving parts – fuses either pop or they don’t. Conversely, a circuit breakers’ operation is a bit more sophisticated, creating the potential for malfunction. Your mileage may vary, but we’re going to side with the experts on this one and use fuses where we can.

You can see we’ve secured our wiring in a location that is away from anywhere fluid may potentially pool. This can be difficult if space is limited and because of the proximity to the radiator.

4) Keep Things Cool, Not Wet. There’s A Difference:

  • “If water is common in the area of the fan, pay attention to drainage. Water will pool in low points in harnesses, so be mindful of low points in hanging loops or angles of insertion for connectors where water may pool.”

Enthusiasts are regularly performing engine swaps and cramming cubic-inches where they were never meant to be. In doing so, wires are fished through tight spaces. Often times, people don’t take into account the hostile environment in which those wires and harnesses live. This tip is all about being cognizant of wire placement – particularly cooling fan wires.

Wires and relays can easily find themselves submerged in fluid because of their proximity to the radiator and coolant. That’s not to mention the fact they can be exposed to the elements if the car in question doesn’t have any fender liners. So, it’s essential to keep your wires and harnesses tucked away from anywhere that water or coolant might pool. Lest we forget – water and electricity don’t mix.

Using dielectric grease on connectors might sound like a good idea, but if you’re dealing with a high-load current, it can actually do more harm than good.

5) Despite What The Parts Store Employee Told You, Don’t Use Dielectric Grease On Fan Plugs:

  • “Don’t use dielectric grease on fan plugs. Fans draw enough current that dielectric grease should not be used. Dielectric grease in fan plugs can liquefy and wick into wires and terminals, causing intermittent connections and arcing/hotspots.”

We know, we know – the prepubescent teenager behind the auto parts store counter told you dielectric grease is mandatory for all electrical connectors. Well, in this case (and many others, no doubt) he’s wrong. Interestingly enough, the very grease you’ve been using to ensure optimum conductivity for all your connections could be detrimental to your cooling system.

As Brent mentioned above, with the high-amperage current running through your fan connections, dielectric grease is unnecessary and could end up melting, thus shorting the circuit.

6) Don’t Rely On Your Memory, Get Yourself A Thermal Switch:

  • “Use temperature control for fans. Some people like to turn on their fans manually, and that isn’t a problem. But, we recommend having a thermal switch installed anyway in case customers forget to turn on their fan manually.”

It’s happened to the best of us. You’re cruising along the highway, and all of a sudden, you feel a cold icicle of sheer terror rip across your very being when you glance at your temperature gauge and see it pegged at 220. You forgot to switch on your fans! An easy mistake to make, but an unnecessary one. Install a thermal switch, and never worry about it again.

7) Test It Before You Trust It:

  • “Test the fan system before use! Bypass the thermal switch, and verify the function of the fan/relay before you start your engine. There’s nothing worse than overheating a brand new build because no one tested the fan system before the first test drive.”

This tip should go without saying, but Brent is right to remind us all. It only takes a few minutes to verify your new fan system works with an auxiliary switch and some test leads. Ensuring your fan and relay are working correctly before hitting the road is just cheap insurance.


8) When To Use A Relay:

“Relays are used with brushed fans, and not used with brushless fans. As brushless fans are growing in popularity, we have had a few customers try to add a relay to a brushless system when a relay isn’t required. We don’t need a relay with brushless fans because they always do a soft start. In a brushless fan system, the fan is connected to constant power – directly to the battery. When the brushless fan receives the command signal to run, it makes a connection internal to the motor and runs. When the command signal goes away, the brushless fans enter quiescent current (sleep) mode.”

First, we should mention it’s not even possible to properly wire a relay to a brushless fan. In order to avoid difficulty and an embarrassing tech line phone call, keep that in mind. The reason brushless fans don’t need a relay is because they don’t require the heavy-duty switching contacts of a relay because there isn’t a high-current draw on startup. So, if you’re looking to upgrade to brushless fans, you can do without the relays.

There you have it, SPAL Automotive Technology’s seven best practices for wiring fans. So, while your car might not be hitting the streets for a few months, you can take that time to double-check and improve your system.

If you’d like to know more about all things cooling, check out the SPAL website at

Article Sources

About the author

Vinny Costa

Fast cars, motorcycles, and loud music are what get Vinny’s blood pumping. Catch him behind the wheel of his ’68 Firebird. Chances are, Black Sabbath will be playing in the background.
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