Crimping vs Soldering 12V Wires: Best Method for Campervan Electrical Connections
The debate between crimping and soldering 12V wires is one of the oldest in vehicle electrical work. Soldering makes a pretty connection. Crimping makes a reliable one.
I started my first van build by soldering every connection — it felt more professional. Within a year, three connections had failed. One snapped off at the solder joint (vibration fatigue). Another had cracked insulation where the solder had wicked up the wire. A third corroded at the exposed copper between the solder and the insulation.
I now crimp every connection with a proper ratchet crimper. Not a single failure in three years.
Why Crimping Wins
| Factor | Crimp | Solder |
|---|---|---|
| Vibration resistance | Excellent | Poor — solder wicks up wire, creating a stress point |
| Pull strength | 80–95% of wire rating | 60–80% of wire rating (wires break at solder edge) |
| Corrosion resistance | Good (sealed crimp) | Poor (solder wicks up, leaving exposed wire) |
| Ease of rework | Easy (cut and re-crimp) | Difficult (must remove old solder) |
| Skill required | Low (with proper tool) | Medium (requires practice) |
| Tool cost | £20–40 (ratchet crimper) | £10–30 (iron + solder) |
| Time per connection | 30 seconds | 2–3 minutes |
| Works in cold | Yes | Yes |
| Needs ventilation | No | Yes (solder fumes) |
When to Solder (and When Not To)
| Connection Type | Use Method |
|---|---|
| Ring terminal to battery | Crimp only |
| Butt splice (joining two wires) | Crimp only |
| MC4 solar connector | Crimp only (factory recommendation) |
| Thin wire to circuit board | Solder only |
| Wire to switch terminal | Either (crimp preferred) |
| Wire to fuse holder | Crimp (factory recommendation) |
| Heat shrink tube seal | Crimp + heat shrink (dual protection) |
Rule: If the connection experiences vibration (every connection in a moving vehicle), crimp it. If it is a static connection (circuit board, permanent junction), soldering is fine.
The Right Crimp Tool
A hammer crimper creates a cold weld that looks connected but has high resistance. A ratchet crimper creates a gas-tight connection that lasts.
| Tool | Cost | Quality | Best For |
|---|---|---|---|
| Combination pliers (Halfords) | £10 | Poor — dies are wrong shape | Emergency only |
| Hammer crimper | £8–15 | Poor — inconsistent pressure | Large battery lugs (with practice) |
| Ratchet crimper (generic) | £15–25 | Good — hex or indent dies | Most van wiring 1.5–6mm² |
| Ratchet crimper (professional) | £40–60 | Excellent — precision dies | All van wiring |
| Hydraulic crimper | £30–50 | Excellent — for 25mm²+ lugs | Battery cables, large inverters |
The minimum: A ratchet crimper with interchangeable dies for:
- 1.5–6mm² insulated terminals
- 6–16mm² non-insulated terminals
- 25–50mm² battery lugs
A £25 ratchet crimper set covers all these.
Crimping Technique
Step-by-Step (Ring Terminal)
- Strip 8–10mm of insulation from the wire. Use a wire stripper — do not use a knife (you nick the copper strands).
- Twist the strands together lightly (just enough to keep them aligned, not tight).
- Select the correct die on the crimper for the terminal size. Most terminals are colour-coded: red (1.5–2.5mm²), blue (4–6mm²), yellow (10–16mm²).
- Insert the wire into the terminal. The insulation should sit flush against the terminal's insulation grip.
- Place the terminal in the crimper die. The solid barrel goes in the crimper, not the insulation grip.
- Squeeze the handles until the ratchet releases. Do not release early — the connection is not complete until full closure.
- Pull on the wire to test. It should not move. If it pulls out, the crimp is bad — cut and re-crimp.
- Apply heat shrink over the crimp and the wire insulation.
Common Crimping Mistakes
| Mistake | Result |
|---|---|
| Wire too long (bare copper visible past the terminal) | Corrosion at exposed copper |
| Wire too short (insulation inside the terminal barrel) | Poor electrical contact |
| Wrong die for terminal size | Loose crimp or damaged terminal |
| Releasing ratchet early | Incomplete crimp — wire can pull out |
| Not pulling test after crimp | Wire pulls out later (vibration) |
| Stripping wire with knife | Nicked strands break under vibration |
Soldering Technique (When Appropriate)
For Circuit Board Connections
- Tin the iron tip with a small amount of solder
- Clean the wire and circuit board pad with isopropyl alcohol
- Apply the iron to the pad and wire simultaneously (1–2 seconds)
- Feed solder into the joint (not directly onto the iron tip)
- Remove the solder, then the iron
- The joint should be shiny and concave — a dull, rough joint is a cold solder joint
For Wire-to-Wire (If You Must Solder)
- Strip 15mm of insulation from both wires
- Twist the wires together (Western Union splice or similar)
- Apply flux to the joint
- Heat the wire (not the solder) — the solder should flow into the wire, not sit on the surface
- Solder must wick into the wire, not pool on the outside
- Cover with heat shrink tubing
Heat Shrink
All connections — crimped or soldered — should be sealed with heat shrink tubing.
| Type | Shrink Ratio | Best For |
|---|---|---|
| Standard polyolefin | 2:1 | General wiring |
| Dual-wall adhesive-lined | 3:1 | Outdoor/exposed connections |
| Clear polyolefin | 2:1 | Connections you need to inspect |
| Marine-grade (with adhesive) | 3:1 | Any connection in a van (condensation) |
Recommendation: Use dual-wall adhesive-lined heat shrink for every connection in a campervan. The inner adhesive melts and seals the connection against moisture. Standard heat shrink leaves a gap at the wire entry point where moisture enters.
Testing Connections
| Test | Method | Good Result |
|---|---|---|
| Pull test | Pull on the wire with moderate force | Wire does not move in terminal |
| Visual inspection | Look at the crimp | No gaps, no exposed copper |
| Voltage drop test | Measure voltage drop across the connection at rated current | Under 0.05V drop |
| Resistance test | Multimeter across the connection | Under 0.01 ohm |
| Thermal test (infrared) | Run rated current for 5 minutes, check temperature | Connection is not hotter than the wire |
FAQ
Q: Can I solder a crimped connection for extra strength? A: No. Solder wicks up the stranded wire and creates a hard stress point. The wire will break at the solder edge under vibration. Crimp only for vehicle wiring.
Q: What is the best crimp terminal brand for campervans? A: Durite (UK brand, available at most factors) or AMP/TE Connectivity (professional). Avoid unbranded Amazon terminals — they use thinner copper that does not hold the crimp.
Q: Do I need to tin the wire before crimping? A: No. Tinning (applying solder) before crimping makes the wire harder and the crimp less effective. Crimp onto clean, untinned copper strands.
Q: What gauge wire needs a hydraulic crimper? A: 25mm² and above benefits from a hydraulic crimper. A ratchet crimper can handle 25mm² but requires significant hand force. For 35mm² and 50mm², use a hydraulic crimper.
Q: Is it OK to use wire nuts in a campervan? A: No. Wire nuts are designed for household AC wiring in junction boxes. They vibrate loose in vehicles. Use crimp connectors or Wago lever nuts (sprung, not screw type).
