What is the 'Post-Insert' Type That Saves You When You Forget the Insulating Sleeve for Bullet Terminals?

Bullet terminals are indispensable for electrical work on motorcycles and cars. However, many people have experienced the mistake of "forgetting to put on the insulating sleeve" after crimping the terminal. In such cases, the "post-insert sleeve," which can be attached after the terminal has been crimped, is very useful. It is easy to use even in places where there is not much slack in the wiring, and it is also compatible with vehicle wiring modifications. This time, we will introduce the basic usage of bullet terminals, as well as the unique advantages of post-insert sleeves.

Bullet Terminals Are Essential for Electrical Wiring Work

In electrical customization for motorcycles and cars, bullet terminals are widely used as a method for connecting wires, such as when extracting power. The biggest feature of bullet terminals is that they ensure reliable conductivity while allowing for easy disconnection when necessary.
For example, when adding accessories such as USB power supplies, grip heaters, or fog lamps, if there is a possibility of removing them in the future, it is more convenient for future maintenance to connect them with bullet terminals rather than soldering the wires directly.
Also, when troubleshooting or replacing parts, it is highly efficient because you can disconnect the wiring like a connector. This ease of handling is a major reason why they have been supported for many years when installing accessories DIY.

Bullet terminals are frequently used for electrical wiring connections along with couplers. They are also frequently used when installing aftermarket electrical accessories. This image shows a bullet terminal used at the connection point between the power generation alternator and the regulator rectifier, using a waterproof type of insulating sleeve.

The Basic Rule for Bullet Terminals: Female on the Positive Side, Male on the Negative Side

There are male and female bullet terminals, and there are rules for their use in vehicle wiring. The basic rule is to use a female terminal on the vehicle's positive wiring side and a male terminal on the negative wiring side. This way, even if the terminal accidentally comes off from a live wire, the female terminal is covered by an insulating sleeve, so it will not short-circuit even if it touches the frame or the vehicle body, keeping it safe.
On the other hand, since the metal part of the tip of the male terminal is exposed, there is a risk of a short circuit if it is used on the positive side and touches the frame or other metal parts.
When cutting existing wiring to install bullet terminals, you may be confused about how to use male and female terminals, but when installing USB power supplies or additional lamps, remember that "the positive side (power side) of the accessory is the female terminal."
Of course, this is just a general idea, and there are exceptions depending on the connection position and circuit configuration. However, if you remember the basic principle of electrical work: "insulate the side that would short-circuit if the bullet terminal came off and touched the vehicle body," it will help prevent trouble.

The image above shows the state after installing a waterproof insulating sleeve, and this is the original alternator wiring before modification. Originally, the entire female terminal is covered with an insulating sleeve, so even if the bullet terminal were to come off, it would not touch the frame or engine.

There Are "Pre-Insert Sleeves" and "Post-Insert Sleeves" for Insulating Sleeves

As you can see from the explanation above, an insulating sleeve is essential when using bullet terminals. Insulating sleeves play a role in covering the metal part of the terminal to prevent short circuits and poor contact. Especially on motorcycles with a lot of vibration, the wiring may move while driving, so insulation treatment is extremely important.
For general insulating sleeves, the mainstream is the "pre-insert sleeve," which is passed through the wire before crimping the terminal and then covered after crimping the terminal. However, in actual work, it is not uncommon to accidentally realize that you forgot to pass the sleeve through after finishing crimping the terminal. Realizing "Oh no, I forgot to put on the insulating sleeve!" and cutting off the terminal that you worked so hard to crimp neatly is a waste of time and parts.
In such cases, the "post-insert sleeve," which can be attached after the terminal has been crimped, is convenient.
As the name suggests, the post-insert sleeve has a structure that allows it to be attached after the bullet terminal has been crimped. Since it is installed by inserting the sleeve from the tip of the terminal, the work procedure is different from that of a normal sleeve, and the shape is completely different from the pre-insert type, where the hole diameter at the rear end is only slightly larger than the wiring.
Its biggest advantage is that it can recover from forgetting to put on the sleeve. Even in situations where you would have to cut the terminal and redo it with a normal sleeve, you can attach it as is with a post-insert sleeve, so you don't have to waste terminals or wiring.
It is also effective when there is no slack in the wiring length. For example, when modifying the vehicle-side harness or working on the actual vehicle in a narrow space, there are cases where the wiring cannot be pulled out much. With pre-insert sleeves, it is essential to pass them through the wiring until the entire bullet terminal is exposed, and depending on the wiring length and work space, it can be difficult to install. However, with the post-insert type, it can be attached from the side of the terminal that has already been crimped, so it is easy to handle even in situations where there is no slack in the wiring.
Similarly, the fact that it is compatible with the modification of existing harnesses cannot be overlooked. When adding or repairing accessory power supplies, there are situations where new terminals are attached to short wires remaining on the vehicle body. In such situations, it is difficult to secure space to pass the sleeve, but post-insert sleeves can respond flexibly.
In addition, reducing rework due to work errors is also a merit. If you repeat "re-crimping" after noticing that you forgot to insert the sleeve, the electric wire may become short or the core wire may be damaged. With post-insert sleeves, you can avoid re-construction due to forgetting to pass it through, which leads to maintaining wiring quality as a result.

A set of pre-insert type insulating sleeves and bullet terminals. In any case, combine them so that the male terminal has a short sleeve and the metal terminal is exposed, and the female terminal is housed within a long sleeve.

It is a rule that pre-insert sleeves must be passed through the wiring before crimping the bullet terminal. While concentrating on the work and attaching many bullet terminals, you may accidentally forget to pass them through first.

To avoid getting in the way when crimping the bullet terminal, the pre-insert type insulating sleeve must be inserted at the base of the wiring. Since the sleeve of the female terminal is long in total length, it becomes quite cramped for short wiring.

When you crimp the bullet terminal and cover it with the insulating sleeve, you can see that the sleeve of the female terminal is more than twice as long as the male terminal. When branching existing wiring, you can see the importance of securing the insertion allowance for the insulating sleeve and that the wiring length required to pass the insulating sleeve is surprisingly necessary.

Use "Pre-Insert Sleeves" and "Post-Insert Sleeves" According to the Application

An example of post-insert sleeves that can be purchased via online mail order. This is a set for male and female terminals, and some products include not only sleeves but also bullet terminals.

Even if it can be inserted from the tip of the crimped terminal, if the inner diameter of the sleeve is simply large and loose against the wiring, it will come off, so the rear part is tightly narrowed. A feature of the post-insert sleeve is that it has a special shape that allows the terminal to be inserted on top of that.

Of course, it does not mean that post-insert sleeves are absolutely superior. Many people prefer the conventional pre-insert sleeves in terms of workability and familiarity, and when performing wiring processing in a mass-production manner, the pre-insert type can sometimes be worked on more smoothly. Also, generally, the pre-insert type has a slimmer sleeve shape than the post-insert type, which has the advantage of finishing the area around the bullet terminal smartly.
However, in electrical customization and repair work on the actual vehicle, there are many cases where the wiring space is more limited than expected. At such times, if you keep post-insert sleeves in your toolbox, there should be times when they will help you.
Bullet terminals are basic parts for DIY electrical work, but they only become safe connections including insulation treatment. Just because you forgot the pre-insert sleeve, it is not recommended to wrap the bullet terminal with vinyl tape. While thoroughly using male and female bullet terminals and attaching insulating sleeves, it is good to make good use of post-insert sleeves according to the work content.

Push the post-insert sleeve from the tip side of the crimped female terminal. Since the pre-insert sleeve has its rear end narrowed to the wiring diameter, it can never be pushed in like this.

As shown in the image, it can be pushed in up to the crimped part. Of course, the tip of the female terminal will not be exposed, so there is no worry of a short circuit even if it is used for the positive power supply side wiring and touches the vehicle body, etc.

What I want to pay attention to is the positive terminal side. In the post-insert type, the hem of the sleeve is wide, and it has a structure that can cover a wider range around the positive terminal.

Since the post-insert sleeve has the male terminal sleeve covered over the female terminal sleeve, the outer diameter is slightly thicker than the pre-insert sleeve. However, it is a great advantage that it can be installed without difficulty even in situations where there is no slack in the wiring length.