Fusing The Circuit: Selecting Switches

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When you add an electrical part to your car (race car, street rod, street-strip car, whatever) such as an electric fan, an electric fuel pump or whatever, there’s almost always a need to splice in a switch. Easy enough. You should be able to go down to your local auto parts store and buy a switch. That’s a no brainer. Right? Maybe not:

Before you pick a switch for a circuit you add to your car, you should stop and ponder the situation a wee bit. One area to contemplate is the choice between a toggle switch and a rocker switch. With a high-quality toggle switch, there's no question if the switch is "on" or "off". Not so with some rocker switches. On the other hand, the chance of accidentally activating or deactivating a circuit is less with a rocker switch when compared to a toggle switch. Bottom line here is, it's easier to accidentally flick a toggle switch than it is a rocker switch. That’s why many race-oriented toggle switches have safety covers – more in the accompanying photos.

The quality of the switch is another question. Today, the market is filled with any number of junk plastic made offshore switches. Needless to say, the life expectancy along with the structural integrity of a cheap, foreign made plastic switch should be questioned in any high-performance application, and that includes your car. High quality switches are readily available. You have to know where to look but they aren't cheap (some examples cost upwards of $40). For example many seasoned racers select switches that were initially designed for aircraft or heavy-duty commercial truck use. Some race parts vendors sell these heavy duty aircraft grade switches (Quick Car Racing Products is one such vendor). This is done for good reason too: The racer or race team can be assured the switch is designed for a lifetime of use, and won't fail under the stresses imposed by a modified car. It’s an idea for you to copy.

When shopping for a switch, an important factor is the rating. Electrical gurus will generally note that the key to switch life is to use a part that is capable of handling the amperage. It's easy to install a cheap, low amp switch in your application but when all is said and done you pay the price because the switch contacts tend to burn out quickly.

That's not the end of it either: The configuration of the switch and where you use it is significant. Many race-bred custom switch panels incorporate a momentary-on starter switch. Here a push button operated SPST (Single-Pole, Single-Throw) turns the starter circuit on when pushed, and off when released. This type of switch is often used as a bump starter button on a racecar where it’s used to set the valves. Many starter switches are covered with a rubber boot to reduce dirty and dust infiltration, but another purpose of the covering is to make the switch different from the rest. That makes it easily identifiable from the others, even with gloved hands.

The work a switch does is important too. Aside from the type of switch you prefer, you should also ponder the mechanics of the switch. Along with the momentary-on starter switch, the next most common arrangement you'll come across is a simple on and off switch. Like a starter switch, this component is also a SPST switch. This is simplest of switch designs, and it only controls one circuit. A SPST switch is equipped with two terminals: One is connected to the battery or power source while the other is connected to the load or component being switched.

Another configuration you'll likely encounter is a "Single-Pole, Double-Throw" or SPDT switch. Like the momentary-on switch, a SPDT switch has only one moveable element inside, but it is equipped with three terminals outside. One of the terminals connects to the battery, but the other two terminals connect to two separate circuits or loads. The design of the switch allows you to switch from one component to another, but not both. Most often, there are three positions found on this switch configuration: They’re “On-Off-On”. Sometimes this arrangement is called a "center-off" switch. A switch such as this can also have a Momentary On-Off-On arrangement. With this format, you can do something like prime a fuel system with the Momentary On feature, then turn the fuel pump "on" after the system is primed. Clever.

Something new in the switch business is the "touch pad" configuration. It’s used by several companies that manufacture racecar electrical control panels. Essentially, switches such as this are similar in format to those you’ll come across in household appliances such as a microwave oven or a modern range. These switches incorporate a large, soft membrane that allows you to operate them at a touch. The advantage to this type of switch in something like a racecar is that it can be operated easily with a gloved hand. But they don’t offer that noticeable “on” or “off” feel that say, a rocker switch provides. As a result (and to ensure the switch isn't accidentally turned on or off), some of the switch panel builders add a series of warning lamps so that you can see when a circuit is “live”.

So far so good, but where do you find high quality switchgear? Try your local aircraft avionics shop. And if you don’t one handy, I’m positive that outfits like Aircraft Spruce and Specialty (www.aircraftspruce.com) can help you out. Ditto with Quick Car Racing Products (www.quickcar.com).


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Some electrical components mandate a relay. This pre-wired single relay from MagnaFuel (part number MP-1025) has a 30-amp rating.

Relay wiring isn’t difficult: With the MagnaFuel relay, the heavy black wire goes to ground. The heavy red wire goes to the battery. The orange wire is routed to the on-off switch (or the vehicle ignition switch). The blue wire goes to the hot side of the electric pump.

Here’s another really common racing switch. It’s a Hurst Line Lock (Roll control) switch. The switch is designed to slip over a common stick shift handle.

This switch is a momentary on switch with a heavy coiled cord. This switch is designed for steering wheel mounting. It can be used for a line lock or transmission brake.

This is a momentary on switch with a long lever. What’s the purpose? It’s a micro switch that can be mounted so that something (for example, a transmission shift lever or throttle linkage) activates it. You can use it to control nitrous activation or for a high gear ignition timing retard. Note the manufacturing location. Good or bad?

This starter bump switch (from Jerry Bickel Race Cars) is a quality momentary on device, fitted with a rubber weather cover. They’re definitely useful when adjusting valves or in the case of a race car, working on the clutch.

The most common fuse you’ll come across today is a blade style or “autofuse”. The majority of today’s cars incorporate this style of fuse.

This is the fuse configuration used on older cars. It’s called a “glass capsule” fuse. Believe it or not, some experts actually prefer this style of fuse over the more modern “autofuse”. The text offers details.

When the time comes to install a circuit or two in a modern production car such as your car, there’s usually no need to push a bare wire under a fuse and keep your fingers crossed that it works. Instead, examine the fuse box closely. This late model GM setup (from a Turbo Buick) has several auxiliary circuits that are already fused. You simply crimp a spade terminal on the wire end and fasten it to the female receptacle in the fuse box. And yes, many early fuse boxes with glass fuses had similar provisions.