If You’ve Ever Started a Car Without a Neutral Safety Switch You Know the Rest of the Story

t’s not much of an accessory, it’s relatively inexpensive, it’s simple to install, and it’s one of those things you really shouldn’t live without. Not having one could cost you a great deal. The Neutral Safety Switch (NSS) is something that every hot rod should include, and for good reason. If you have ever driven a hot rod without an NSS 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 an NSS within a car’s starting sequence. I have seen beautiful hot rods rearrange cinder block, 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 NSS.

A Little Background

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. 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, four-speed, Posi rearend, and disc brakes, outfitted with safety goodies that I hadn’t seen on my 1950 Studebaker Commander or my 1956 Chevy. (I didn’t order A/C or any power accessories because that robbed horsepower and I was a drag racer.) For 1967 my Chevy II 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 on board. Those of you who have been at this hot rod game for a while may recall in December 1971 General Motors recalled over 6.68 million 1965-1970 Chevrolets with defective V-8 engine mounts—and that included my 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. Although most production vehicles have had an NSS 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 NSS, 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.

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 NSS when the proper conditions are met and to send current.

However, this only works if the trans is in Park or Neutral. Basically, the NSS 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.

When the NSS Goes Bad—Troubleshooting

An NSS is like any component on your hot rod: It can go bad over time, some of the common reasons 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 NSS is easy to find and swap out.

First thing to check when looking for a bad NSS is a “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 get the switch replaced quickly.

A malfunctioning NSS is oftentimes the result of the switch being out of adjustment. (Lokar has explicit instructions, available online on how to set up or check an NSS.) Lokar recommends you check the function of the NSS by testing for continuity by connecting an ohmmeter lead to each stud on the NSS. When adjusted correctly, you will only have continuity between the two switch studs when the shifter lever is in Park or Neutral.

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 NSS please make sure the battery is disconnected and the wheels/tires are blocked or the car is safely resting on floorjacks. Do not perform the adjustment tasks with the engine running. Again, I have heard the stories and they never end well.

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!

2. 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. 

4. Pictured is 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.

6. Here is an NSS from American Autowire that is for a manual transmission that is used on a 1969 Chevy Chevelle or El Camino(PN 01993490).

8. What’s convenient about the Lokar NSS is that it attaches to the shifter mechanism underneath the lever boot. All Lokar automatic transmission shifters come with a neutral safety switch. All it takes is a 7/8-inch wrench/socket to install or remove.

9-10. 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.