A good crimp creates a gas-tight mechanical connection that will outlast the vehicle. A bad crimp creates a high-resistance joint that corrodes, heats up, and eventually fails — sometimes years later, in a way that's nearly impossible to diagnose.
Most electrical problems in old vehicles trace back to bad crimps. This guide covers why crimps fail and how to make ones that don't.
Why Crimps Fail
Wrong Tool
The crimping tool matters more than most people realize. The cheap red/blue/yellow crimpers from the auto parts store are designed for insulated crimp connectors (butt splices, ring terminals). They crush the terminal instead of forming it properly around the wire.
Open barrel terminals — the kind used in automotive connectors — require a crimper that folds the wings of the terminal around the wire in a specific pattern. Using the wrong tool makes a connection that looks okay but isn't mechanically sound.
Wrong Size
Terminals are sized for specific wire gauges. A 20-22 AWG terminal on 18 AWG wire won't crimp tight enough. An 18 AWG terminal on 22 AWG wire will be loose. The terminal should fit snugly on the stripped wire before you crimp.
Bad Strip
If you nick the copper strands when stripping, you've weakened the wire at exactly the point that will see the most stress. Nicked strands also don't compress properly in the crimp. Use sharp strippers and the correct gauge setting.
Wrong Position
The wire has to be in the right spot relative to the terminal. Too far in and the insulation is in the crimp area. Too far out and the conductor crimp doesn't grab enough wire. Open barrel terminals have two crimp areas — one for the conductor and one for the insulation — and each needs to land in the right place.
The tug test: After every crimp, tug firmly on the wire. If it pulls out, the crimp failed. Better to find out now than when the truck is on the side of the road.
Terminal Types
Open Barrel
Open barrel terminals are what you'll find in factory automotive connectors. They're called "open barrel" because the crimp area is open (not enclosed) before crimping.
Two crimp zones:
- Conductor crimp — The rear wings fold around the bare copper strands. This is the electrical connection.
- Insulation crimp — The front wings fold around the wire insulation. This is the strain relief.
Both crimps are important. The conductor crimp makes the electrical connection. The insulation crimp keeps flex and vibration from stressing the conductor crimp.
Closed Barrel
Closed barrel terminals have an enclosed crimp area — you insert the wire into a tube. Common on ring terminals, spade terminals, and butt splices.
These are easier to crimp (less positioning required) but harder to inspect. You can't see the wire inside to verify the crimp quality.
Crimping Open Barrel Terminals
Step 1: Strip the Wire
Strip the insulation to match the terminal's conductor crimp area — usually about 3-4mm. The bare conductor should fill the conductor crimp wings without extending beyond them.
- Use quality strippers set to the correct gauge
- Don't nick the strands
- Don't twist the strands unless the terminal requires it
Step 2: Position the Wire
Insert the wire into the terminal so that:
- The bare conductor sits fully within the conductor crimp wings
- The insulation sits within the insulation crimp wings
- A tiny bit of bare conductor may be visible in front of the conductor crimp (but not much)
Step 3: Crimp the Conductor
Using a proper open barrel crimper:
- Place the terminal in the correct die (sized for the terminal)
- Verify the wire hasn't shifted
- Squeeze the crimper fully — don't release early
- The wings should wrap around the conductor in a B-shape or heart shape when viewed from the end
Step 4: Crimp the Insulation
Repeat for the insulation crimp wings. This crimp should be firm but not crushing — you're gripping plastic, not making an electrical connection.
Step 5: Inspect
Look at the finished crimp:
- Wings should be fully wrapped, not sticking up
- No conductor strands should be outside the crimp
- Insulation should be gripped but not cut through
- Terminal shouldn't be deformed or cracked
Step 6: Tug Test
Pull firmly on the wire. It should not move or come out. If it does, cut it off and start over.
No solder on crimps. Adding solder to a crimp seems like it would make it stronger, but it actually makes it worse. Solder wicks up the strands and creates a rigid section next to a flexible section. The wire will break at that transition point from vibration. A proper crimp alone is superior to a soldered crimp.
Common Mistakes
"It'll Be Fine"
A crimp that feels a little loose, has one strand sticking out, or didn't quite close all the way is not fine. It will fail eventually. Redo it.
Using Pliers
Pliers don't form the terminal correctly. They just smash it flat. The connection might work initially but will develop high resistance over time.
Reusing Terminals
Once a terminal is crimped, the metal is work-hardened and deformed. Cutting off the old wire and re-crimping usually results in a weak connection. Use new terminals.
Crimping Stranded and Solid Together
If you're splicing and one wire is stranded and one is solid, the crimp won't grab both properly. Use terminals appropriate for each wire type, or splice using a method appropriate for mixed wire types.
Recommended Tools
Budget (Under $50)
Engineer PA-09 or similar ratcheting open barrel crimper. Won't release until you've completed the crimp cycle, which helps ensure consistent crimps.
Professional ($50-150)
IWISS or Hozan crimpers with interchangeable dies for different terminal sizes. More precise control and better longevity.
What to Avoid
The stamped steel crimpers that come free with terminal assortments. Also the "universal" crimpers with multiple grooves stamped into the jaws — they're designed for insulated terminals, not open barrel.