Terminals, Connectors & Heat Shrink

What it is

Vehicle wiring is joined with crimp terminals (ring, spade, butt splice, bullet and quick-disconnect), multi-pin connectors (sealed or unsealed) and heat-shrink tubing that insulates and seals the joint. On fleet equipment, water and road salt are the main enemies, so sealed parts are the normal choice outside the cab.

How to identify

Insulated terminals have a colored sleeve over the crimp barrel. The color shows the wire gauge range. Heat-shrink terminals have a clear or colored sleeve that shrinks and often shows adhesive at the ends after heating. Sealed connectors have rubber seals on each wire and a seal between the two halves. Unsealed connectors have open wire entries.

Insulated terminal colors

Larger battery and starter cables use uninsulated lugs sized by cable gauge and stud size. See the battery cable SGT and SGX sheet.

Heat-shrink basics

• Shrink ratio (2:1, 3:1, 4:1) is how far the tube shrinks from its supplied size. Higher ratios cover irregular shapes and fit over connectors.
• Single-wall tubing insulates and strain-relieves only.
• Dual-wall, adhesive-lined tubing has a glue layer that melts and seals. This is the type to use outside the cab.
• Pick a tube whose recovered size is smaller than the wire, and whose supplied size slides over the joint.

Key points

• Use the crimp tool made for the terminal type. Insulated, non-insulated and open-barrel terminals each need different dies.
• A good crimp needs the correct wire strip length. Wire strands should be visible at the front of the barrel but the insulation should not be in the crimp.
• Sealed connectors need the correct wire seal size for the wire insulation diameter, and cavity plugs in unused positions.
• Apply dielectric grease to connector seals where the maker calls for it. It does not replace a seal.
• Use tinned copper terminals in corrosive locations.

Common mistakes

• Crimping with pliers instead of a ratcheting crimper.
• Using single-wall heat shrink outside the cab.
• Leaving empty cavities in a sealed connector unplugged.
• Using a terminal one size too large so the wire pulls out.
• Twisting and taping wires instead of a sealed splice.

Governing standards: SAE J163 (low-tension wiring and cable terminals and splice clips) and SAE J1128 (low-voltage primary cable); connector and terminal maker's crimp specifications. See the primary wire gauge reference.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.