What is a Neutral Safety Switch and Why it is Important

By Brian Brennan

It’s not much of an accessory, relatively inexpensive, simple to install, and one of those things you really shouldn’t live without. Not having one could cost you a great deal. The Neutral Safety Switch is something that every hot rod should include, and for good reason.

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02 OE style neutral safety switch from Bowler Performance Transmissions
Here is an example of an OE part that’s offered by Bowler Performance Transmissions. It correctly activates the starter only in the Park and Neutral positions. Extra benefit is the provision for the reverse (backup) lights.

If you have ever driven a hot rod without a Neutral Safety Switch you understand what can happen should you forget to go through your “pre-start checklist.” I have seen firsthand the damage and injury that can be caused when there isn’t a Neutral Safety Switch within a car’s starting sequence. I have seen beautiful hot rods rearrange cinder blocks, jump off the ramps on a trailer, and, worst of all, an innocent bystander severely injured. You never want to be responsible for something like this—you will always remember your lapse in good judgment. We checked in with American Autowire, Bowler Performance Transmissions, and Lokar Performance Products to gather some info on the Neutral Safety Switch.

Where did the Neutral Safety Switch Come From?

03 Bowler Performance Transmission 4L60E with a neutral safety switch
Again, from Bowler here is the kit installed that will work on a 4L60E and 4L80E MLP/PRNDL switch with either four and seven PIN connectors.

All of us are familiar with SEMA and have attended the show more times than we can count. The SEMA show came into being in 1963 and it was right about this time that one can trace the movement of safety equipment from racing to street cars.

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During the ’60s the brand-new cars would be unveiled at the local new car dealership in September. All of us first noticing the horsepower numbers did recognize the rapid growth of the safety equipment that was coming along for the ride, so to speak. I remember my first new car, a 1967 Chevy II Nova SS, with its 327 engine, four speed transmission, Posi rear end, and disc brakes, outfitted with safety goodies that I hadn’t seen on my 1950 Studebaker or my 1956 Chevy. (I didn’t order A/C or any power accessories because that robbed horsepower and I was a drag racer.)

04 where is the neutral safety switch located on a 4L60E
Pictured is an example of Where is the neutral safety switch located on a 4L60E and 4L80E series of transmissions and the red arrows point to the threaded holes that allow the NSS to be attached to the external case.

For my 1967 Chevy II it came equipped with a dual master cylinder braking system along with a warning lamp, a four-way hazard warning flasher, side marker lights, shoulder belts, and a fully collapsible energy-absorbing steering column to go along with what was already onboard. Those of you who have been at this hot rod game for a while may recall in December 1971, that General Motors recalled over 6.68 million 1965-1970 Chevrolets with defective V8 engine mounts—and that included my 67 Chevy II! (NHTSA Recall 71-0235, now 71V-235.)

Something about the left motor mount breaking, the engine would torque, and the throttle would stick wide open. Even I could see this problem. Common safety devices found in motorsports, such as seatbelts and disc brakes, were invented for motorsport applications and found their way into production vehicles.

05 Where is the neutral safety switch located on TKO Five speed Transmission
Pictured: Where is the neutral safety switch located on a TKO five-speed (new TKX should be similar) that is equipped with an onboard NSS (circled in red). Designed to be easily connected in line with your starter solenoid trigger to eliminate the need for a clutch pedal–mounted switch, the downside is the connector used on the harness no longer has a mate, which means that the end gets clipped off and you hardwire it in or utilize a two-pin Weather Pack connector instead.

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Although most production vehicles had a Neutral Safety Switch as early as the late ’50s, their use on manual transmissions was mandated by the SFI Foundation and became commonplace in the early ’80s on all production vehicles.

What is a Neutral Safety Switch

I’m guessing everyone knows what an NSS does but just in case there may be any lack of clarity let’s explain. The Neutral Safety Switch, basically a relay, once triggered, allows the electrical current to cycle from the ignition switch to the engine starter through the ignition system, which in turn activates the ignition process. This is done to prevent damage to the starter motor and the transmission, but most importantly to reduce the potential of inflicting damage to your hot rod or your buddy.

06 clutch pedal mounted Neutral Safety Switch essentially universal for Hot Rods
Pictured is a clutch pedal–mounted NSS. It’s universal in its approach but can easily be made to work in a hot rod application.

Otherwise, the electrical pathway is open and no current can pass. On an automatic transmission, the switch can be internal or oftentimes mounted to the side of the transmission itself, connected to the shift linkage. This is what tells the Neutral Safety Switch when the proper conditions are met and to send current.

However, this only works if the trans is in Park or Neutral. Basically, the Neutral Safety Switch allows you to start your hot rod in either Park or Neutral when using an automatic transmission. On manual transmissions, there’s a switch with a similar function on the clutch pedal, called the clutch safety switch. This ensures that a manual transmission hot rod can’t be started unless the clutch pedal is depressed.

07 Neutral Safety Switch from American Autowire for a 1969 Chevrolet Chevelle or El Camino
Here is an NSS from American Autowire that is for a manual transmission that is used on a 1969 Chevrolet Chevelle or El Camino (PN 01993490).

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How To Check If Neutral Safety Switch Is Bad—Troubleshooting

A Neutral Safety Switch is like any component on your hot rod: It can go bad over time for any number of reasons but some of the common ones are age, accumulated dirt, corrosion, or damage to the wiring. As long as the wire hasn’t become chafed, broken (especially inside its casing), or some other baddie along its route, the Neutral Safety Switch is easy to find and swap out.

First thing to check when looking for a bad Neutral Safety Switch is what is referred to as “neutral ground.” If your engine starts either in Park but not Neutral or the other way around odds are the switch is bad. Also, if it starts in any of the gears then the switch could also be the dilemma. Another quick check is to wiggle or slightly move the shifter to get the engine to start. In all of these situations, replace the switch quickly.

08 Lokar Performance Products neutral safety switch
Here we have an example of the Lokar NSS with mounting washer (PN S-68154).

Let Me State the Obvious

Also, before changing the switch, make sure you’ve ruled out a bad wiring, bad selector, dash cluster, or other problem with the linkage or transmission itself. From a safety standpoint before swapping out or installing your Neutral Safety Switch please make sure the battery is disconnected and the wheels/tires are blocked or the car is safely resting on floor jacks. Do not perform the adjustment tasks with the engine running. Again, I have heard the stories and they never end well.

09 Lokar Shifter with a neutral safety switch
What’s convenient about the Lokar NSS is that it attaches to the shifter mechanism underneath the lever boot and all is inside the car and easy to reach. All it takes is a 7/8-inch wrench/socket to install or remove.

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Well, there you go. It may be the simplest and one of the least-expensive projects you will perform on your hot rod but you do not want to skip it, take a shortcut, or do an improper installation. This could turn out to be the most expensive and disheartening project that you will ever have to do a second time! MR

10 Lokar bracket and Lokar shifter for hot rod
The Lokar bracket and shift lever mechanism is all very easy to reach from within the car. Even with carpeting in place the NSS can be easily gotten to once the shift boot is removed.
11 Lokar Performance Products integrated Neutral Safety Switch
The Lokar bracket and shift lever mechanism is all very easy to reach from within the car. Even with carpeting in place the NSS can be easily gotten to once the shift boot is removed.
12 Installing the new neutral safety switch from Lokar Performance Products
One wire goes from the starter solenoid to the NSS and the other wire goes to the ignition switch. It’s a “ball” switch and the wires can be reversed with no issue—closed in the Park and Neutral position and open through the remainder of your transmission gears.

American Autowire
(800) 482-9473

Bowler Performance Transmissions
(618) 943-4856

Lokar Performance Products
(877) 469-7440

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