Why is crimping of terminals necessary and why ordinary pliers are not suitable
Every car owner sooner or later faces the problem of oxidized or loose contacts in the car's electrical system. This is especially critical for battery terminals, starter and generator, where poor contact leads to loss of voltage, overheating and even fire. Ordinary pliers or a hammer and chisel are not helpful here - they deform the metal unevenly, creating microcracks that only worsen the problem over time.
Special crimping pliers (or crimpers) solve this problem radically differently. They provide uniform compression terminals around the wire, creating a gas-tight connection that will not oxidize for years. The main advantage is a crimped terminal can withstand vibrations and temperature changes 3-5 times better than a soldered or bolted connection. This is especially important for modern cars with high current consumption (start-stop systems, powerful audio systems, heating).
But not all ticks are the same. Cheap Chinese models often give a “accordion effect” - when the metal of the terminal is crushed in waves, rather than tightly fitting the wire. This leads to false contact, which will appear after several months of operation. How to avoid such a mistake and choose a tool that will last for decades - read on.
Types of crimping pliers: what tasks each type solves
The market offers more than 10 types of crimping pliers, but only 4 main categories are relevant for automotive electrics. Their difference is in the shape of the sponges, compression force and purpose. Let's take a closer look:
- 🔧 Universal crimpers - Suitable for most automotive terminals (ring, fork, pin). They have adjustable force and replaceable dies. An ideal choice for home use if you do not specialize in one type of connection.
- ⚡ Hydraulic pliers — used for crimping thick power cables (from 16 mm²). Provide up to 10 tons of force, which is critical for high-voltage systems in electric vehicles or trucks. The downside is the high price and cumbersomeness.
- 🔌 Terminal blocks for battery terminals — a specialized tool for crimping lead lugs on a power cable. They often come complete with a set of terminals for different diameters.
- 📡 Microcrimpers — for thin wires (0.25–6 mm²) used in signal circuits (sensors, CAN bus, audio system). They provide precise crimping without deformation of the core.
It is important to understand that sponge shape must exactly match the terminal type. For example, for ring tips you need pliers with hexagonal matrix, and for fork - with flat trapezoidal. Using the wrong tool results in:
⚠️ Attention: If after crimping the terminal there are visible gaps between the metal and the wire, the connection will last no more than a year. In conditions of high humidity (for example, in the engine compartment in winter), such a contact will oxidize in 2-3 months.
Professional auto repairmen often use ratchet pliers (for example, Knipex PZ 35 or Hozan P-747). They fix the force at the end point, preventing the terminal from being “underpressed.” Simpler models are also suitable for amateur repairs, but with mandatory testing of crimp quality (more on this in the testing section).
Top 5 brands: which pliers professionals choose
The quality of crimping depends 80% on the tool. Cheap pliers (up to 1000 ₽) are often made of soft steel, which becomes deformed after 50-100 crimps. Professional models last for decades and give perfect results the first time. Here is a rating of brands trusted by auto electricians:
| Brand | Model | Type | Price, ₽ | Features |
|---|---|---|---|---|
| Knipex | PZ 35 | Universal | 8 000–10 000 | Ratchet mechanism, replaceable dies, crimping up to 10 mm² |
| Hozan | P-747 | For battery terminals | 6 500–7 500 | Reinforced design, crimped lead lugs |
| Weidmüller | Z 100 | Microcrimper | 4 000–5 000 | Precise crimping for wires 0.14–6 mm², ergonomic handle |
| JTC | 4149 | Hydraulic | 12 000–15 000 | Force 10 tons, for cables up to 70 mm² |
| Jonard | C-300 | Universal | 3 000–4 000 | Budget option with acceptable quality |
If your budget is limited, pay attention to pliers from Force or Stayer (domestic brands). They are cheaper than imported analogues, but with proper use they last 3-5 years. The main thing is to avoid “no-name” instruments from China, where even the brand is unknown.
Professional advice: Before purchasing, check to see if your chosen brand has a service center in your area. For example, Knipex and Hozan They give a lifetime guarantee on their pliers, but to activate it you need a receipt and a product passport.
Before using new pliers for the first time, lubricate the hinge mechanism with graphite grease - this will prevent squeaking and corrosion, and will also extend the life of the tool.
Step-by-step instructions: how to properly crimp terminals
Even the most expensive pliers will not save you from poor contact if you violate the crimping technology. Here step-by-step algorithm, which guarantees a reliable connection:
- Wire preparation
Strip the insulation 5–7 mm more than the depth of the terminal sleeve. Use stripper (insulation stripping tool) rather than a knife - this will prevent cuts to the wires. Twist the wires of the harness tightly, but without twisting.
- Terminal selection
The diameter of the sleeve must correspond to the cross-section of the wire. For example, a 4 mm² cable requires a terminal marked
4 AWG. Using the terminal “to grow” will lead to play, and “butt” will lead to damage to the conductors. - Pre-fixation
Insert the wire into the terminal until it stops. If the sleeve is too wide, place a thin copper wire for density. This is a temporary solution - ideally you need to select the exact size terminal.
- Crimping
Place the terminal in the pliers matrix with the sleeve seam on top. Squeeze the handles until they click (for ratchet models) or until they stop. Do not allow skew - this will deform the terminal.
- Quality control
Pull the wire along the axis of the terminal. If it does not slip out, the crimp is successful. Also inspect the liner: there should be no cracks or uneven dents on it.
For visual inspection use lumen test: Hold the crimped terminal to a bright light. If you can see gaps between the wire and the metal, repeat the crimping or replace the terminal.
Stripped the insulation without cutting the cores|
Checked the cross-section of the wire and the terminal |
I made sure that the terminal is free of defects (cracks, corrosion)|
Chose the correct matrix on the pliers |
I checked the crimping force (until it clicks/stops) -->
⚠️ Attention: Never crimp terminals that have been previously soldered or coated with acid (for example, after soldering with rosin). When heated, the remaining flux will turn into a dielectric, and the contact will disappear after a few weeks.
Common mistakes and how to avoid them
Even experienced craftsmen sometimes make mistakes when crimping, which lead to overheating of contacts or circuit break. Here are the most critical of them:
- 🔥 Incorrect choice of terminal material
For copper wires use tinned terminals (tin-coated), and for aluminum - aluminum-copper. Mixing materials (for example, an aluminum terminal on a copper wire) leads to galvanic corrosion.
- ⚡ Crimping by eye
Without fixing the force (as in ratchet pliers), there is a high risk of under-pressuring or pinching the terminal. A pinched terminal breaks due to vibration, and an under-clamped terminal oxidizes.
- 🛠️ Using damaged pliers
If there are chips or wear on the jaws of the pliers, they deform the terminal unevenly. Check the tool before work: the dies must close without gaps.
- 🔌 Ignoring isolation
After crimping, the exposed sections of the wire must be covered with heat shrink tube or electrical tape. Otherwise, moisture will penetrate the joint and it will oxidize within 1–2 months.
Another common mistake is multiple crimping of one terminal. Each new crimp deforms the metal, reducing its strength. If it doesn’t work the first time, it’s better to get a new terminal.
What to do if the crimped terminal still gets hot?
If after crimping the terminal heats up under load, the problem may be:
1. Insufficient wire cross-section (for example, the terminal is 6 mm² and the wire is 4 mm²).
2. Oxidation of the contact surface - Clean the terminal and wire with sandpaper before crimping.
3. Poor contact at the attachment point (for example, the nut on the battery is not tightened).
For diagnostics use thermal imager or an infrared thermometer - heating more than 50°C during starter operation indicates a problem.
Connection testing: how to check crimp quality
A crimped terminal may look perfect but still have high contact resistance. To avoid surprises, use these verification methods:
- Visual inspection
There should be no cracks, sharp edges or asymmetrical dents on the terminal. The seam of the sleeve must be evenly crimped along its entire length.
- Mechanical test
Pull the wire along the axis of the terminal with a force of 10–15 kg. If it does not slip out, the crimp is secure. For thin wires (up to 2.5 mm²), a force of 3–5 kg is sufficient.
- Electrical measurements
Use the multimeter in mode
milliohmmeter(resistance measurement). The resistance between the wire and the terminal should be close to zero (no more than 0.01 Ohm). For accurate measurements use four wire method (excludes the error of the probes). - Thermal test
Connect a load (such as lights or a fan) and check the terminal temperature after 10-15 minutes. Heat above 40°C indicates poor contact.
For critical connections (such as battery power cable), it is recommended to use ultrasonic flaw detector. It reveals microcracks invisible to the eye. In a garage, visual inspection and resistance measurements are sufficient.
If the resistance of the crimped terminal exceeds 0.05 Ohm, the connection is considered defective and must be redone. This is the threshold value for most automotive circuits.
Alternatives to crimping: when to use soldering or welding
Crimping is not the only way to connect wires. In some cases, it is more appropriate to use soldering or welding. Here is a comparison table:
| Method | Pros | Cons | When to use |
|---|---|---|---|
| Crimping | Fast, does not require heating, reliable against vibrations | Requires special pliers and terminals | 90% car connections |
| Soldering | Low resistance, sealing | Brittle compound, oxidizes over time | Signal circuits (CAN, LIN) where vibrations are minimal |
| Welding | Maximum strength, no oxidation | Difficult to do without equipment | Repair of harnesses in high humidity conditions |
| Twist | No tools required | Unreliable, prohibited by PUE | Only as a temporary solution |
In automotive electrics crimping is preferable in 90% of cases, especially for power circuits. It is advisable to use soldering only for thin signal wires (for example, when repairing an oxygen sensor harness) where minimal resistance is important. Welding is justified under extreme load conditions (racing cars, SUVs).
If you decide to solder, use low temperature solder (for example, POS-61) and acid free flux (for example, FKET). After soldering, be sure to insulate the connection with heat shrink - this will prevent corrosion.
FAQ: answers to frequently asked questions
Can I crimp the terminals with regular pliers?
Technically it is possible, but the result will be unreliable. The pliers do not apply even force, causing the terminal to deform unevenly and cause poor contact over time. Suitable for one-time work, but for permanent repairs it is better to buy specialized pliers.
Which terminal color should I choose: red, blue or yellow?
The color of the terminal indicates its material and purpose:
- 🔴 Red — tinned (tin-lead coating), for copper wires.
- 🔵 Blue - aluminum-copper, for aluminum wires.
- 🟡 Yellow — brass, universal, but less resistant to corrosion.
For automotive electrics, red terminals are optimal.
Do I need to lubricate the terminals after crimping?
Yes, but not with any composition. Use conductive lubricants (for example, Liqui Moly Kupfer-Spray or Molykote HSC Plus). They prevent oxidation and reduce resistance. Ordinary lithol or solid oil are not suitable - they collect dust and over time turn into an abrasive.
What to do if the crimped terminal starts to heat up?
Urgently disassemble the connection and check:
- Correspondence of wire cross-section and terminal.
- Quality of crimping (are there any gaps).
- Cleanliness of contact surfaces (oxidation, dirt).
If the terminal is deformed, replace it. A hot contact can melt the insulation and cause a fire!
Is it possible to crimp terminals on high voltage wires (for example, for EV)?
For high voltage systems (from 60V) required special pliers with a force of 8 tons and terminals with 1000V+ insulation. Regular car crimpers are not suitable - they will not provide the required crimping force. Pay attention to the models Knipex 97 53 180 or Hozan P-750.