Motorsport Harness Materials Checklist

This motorsport harness materials checklist explains the common products used when building an EFI wiring harness, ECU loom, engine bay harness, PDM wiring system or custom automotive electrical setup.


A good harness is not just wire and connectors. The finished job depends on choosing the right wire, sleeving, heatshrink, terminals, splices, labels, tooling and documentation before the harness is built.


Quick Answer

For a professional motorsport wiring harness, start with M22759/32 Tefzel wire, protect the loom with Raychem DR25, use Sumitomo W5DL or Raychem ATUM for sealing and strain relief, choose quality sealed connectors, use the correct terminals and splices, then label and document every circuit.

Motorsport Harness Materials Checklist

The table below gives a practical checklist of common materials used in motorsport and custom automotive harness builds.

Material Main Purpose Common Use Why It Matters
M22759/32 Tefzel wire Main conductors ECU wiring, sensors, injectors, ignition, CAN, PDM outputs Lightweight, compact and suitable for professional harness work.
Raychem DR25 Outer harness sleeving Engine bay looms, ECU harnesses, branches and main trunks Protects the wire bundle from abrasion, heat, fluids and general engine bay conditions.
Sumitomo W5DL SCL-style adhesive-lined sealing Harness ends, transitions, breakouts, splices and strain relief Helps seal and support harness sections where adhesive-lined heatshrink is required.
Raychem ATUM Adhesive-lined sealing and repair Moisture sealing, repairs, connector-to-cable transitions and strain relief Useful where a flexible adhesive-lined seal is needed.
Deutsch connectors Sealed electrical connection Engine bay sensors, accessories, lighting, PDM outputs and chassis wiring Reliable sealed connectors make the harness easier to service and diagnose.
Motorsport circular connectors Bulkhead and professional harness connection Firewall connectors, engine harness disconnects and removable sub-looms Useful for clean, compact and serviceable motorsport harness layouts.
Closed barrel splices Permanent wire joins Sensor 5V joins, sensor ground joins, power distribution and branch splices Correct splices make harness joins stronger, cleaner and more reliable.
Labels and identification Circuit identification Wire labels, connector labels, branch labels and service documentation Good labels make fault finding, repairs and future upgrades much easier.
Lugs and power terminals High-current connections Battery cable, earth straps, alternator cables, PDM feeds and fuse box feeds High-current wiring needs proper lugs, correct crimping and strain relief.
Harness documentation Build record and service reference Pinouts, wire colours, connector views, circuit names and fuse details A harness without documentation becomes difficult to diagnose later.

Wire Selection

M22759/32 Tefzel wire is commonly used in motorsport harnesses because it is compact, lightweight and suitable for professional wiring work. Choose the wire size based on current draw, circuit type, cable length, voltage drop and connector terminal size.

Common wire planning points:

  • Use smaller wire sizes for ECU inputs, sensors, CAN bus and signal circuits.
  • Use larger wire sizes for injectors, coils, solenoids, pumps, fans and PDM outputs.
  • Check that the wire size suits the connector terminal being used.
  • Plan wire colours before cutting the harness.
  • Label circuits clearly during the build, not after everything is finished.

Harness Sleeving

Raychem DR25 is normally used as the outer sleeving over motorsport wire bundles. It gives the harness a clean finish and helps protect the wiring from abrasion, heat, fluids and general engine bay conditions.

Use DR25 for:

  • Main harness trunks
  • Engine bay looms
  • ECU harnesses
  • Sensor branches
  • Injector and ignition branches
  • PDM and power distribution wiring
  • Chassis wiring sections

DR25 is not adhesive-lined, so it does not seal the harness ends by itself. For sealed ends, transitions and strain relief, use W5DL, ATUM, moulded boots or other suitable finishing products.

Sealing and Strain Relief

Adhesive-lined heatshrink is used where the harness needs sealing, support or strain relief. This is especially important at harness ends, branch transitions, connector backshells, splices and repaired sections.

Use Sumitomo W5DL for:

  • SCL-style adhesive-lined sealing
  • Harness end sealing
  • Breakouts and transitions
  • Splice protection
  • Firm strain relief
  • Connector backshell-to-cable transitions

Use Raychem ATUM for:

  • Adhesive-lined sealing
  • Moisture protection
  • Cable repairs
  • Connector-to-cable transitions
  • General strain relief
  • Small harness repairs and finishing work

Connector Selection

Connector choice depends on the circuit, environment, current draw, pin count, sealing requirement and how often the harness may need to be disconnected. Engine bay wiring should use connectors that suit heat, vibration, moisture and service access.

Common connector choices:

  • Deutsch DTM for small signal and low-current circuits.
  • Deutsch DT for general automotive and motorsport wiring.
  • Deutsch DTP for higher-current circuits.
  • Motorsport circular connectors for bulkheads, engine harnesses and removable sub-looms.
  • OEM-style connectors when matching factory sensors, coils, injectors or modules.

Always match the wire size to the terminal range. Do not force oversized wire into a terminal that is too small, and do not use wire that is too small for the terminal to crimp correctly.

Terminals, Splices and Lugs

Terminals and splices are just as important as the connector housing. A good-looking harness can still fail if the terminals are wrong, the crimp is poor or the splice is overloaded.

Checklist:

  • Use the correct terminal for the connector series.
  • Use the correct terminal size for the wire.
  • Use proper crimp tooling where possible.
  • Use sealed splices or adhesive-lined heatshrink where moisture protection is required.
  • Use proper lugs and crimp tooling for battery cable and high-current feeds.
  • Check pull strength and inspect crimps before final assembly.

Labels and Documentation

Labels and documentation make the harness easier to install, service and fault-find later. This is especially important on aftermarket ECU wiring, PDM systems, CAN wiring and custom vehicle builds where there may be no factory wiring diagram.

Document these items:

  • Connector names and locations
  • Connector pinouts
  • Wire colours and wire sizes
  • Splice locations
  • Fuse and relay details
  • PDM output assignments
  • ECU input and output assignments
  • CAN bus wiring and termination points

Basic Harness Build Order

A good harness is planned before it is built. The order below is a practical way to approach a custom motorsport wiring harness.

Step Task Why It Matters
1 List every circuit Prevents missing sensors, outputs, power feeds or grounds.
2 Choose wire sizes and colours Makes the harness easier to build, trace and document.
3 Choose connectors and terminals Ensures the wire size, current rating and pin count all match.
4 Plan branches and transitions Allows DR25, W5DL, ATUM, boots and labels to be installed in the correct order.
5 Cut, label and lay out wiring Reduces mistakes during assembly.
6 Crimp terminals and splices Creates reliable electrical connections.
7 Fit sleeving and heatshrink Protects the harness and finishes the build properly.
8 Test every circuit Finds faults before the harness is installed in the vehicle.

Common Mistakes

  • Buying wire before planning the full circuit list.
  • Choosing connector housings before checking terminal wire size range.
  • Using DR25 but forgetting adhesive-lined heatshrink or boots for the ends.
  • Not allowing enough service length at sensors and connectors.
  • Not labelling wires before sleeving the harness.
  • Using poor-quality crimp tools on critical terminals.
  • Not documenting splices and pinouts.
  • Building the harness before checking sensor locations and engine movement.

Practical Planning Tips

  • Plan the harness on paper before ordering materials.
  • Order extra wire and heatshrink so you are not short halfway through the job.
  • Choose connector families that are easy to source replacement terminals for.
  • Keep sensor wiring away from ignition, alternator and starter cables where possible.
  • Use service loops where sensors or engine movement require flexibility.
  • Document everything while building the harness, not after the vehicle is finished.

Shop Motorsport Harness Materials

12Volt Motorsports supplies Tefzel wire, Raychem DR25, Sumitomo W5DL, Raychem ATUM, connectors, sensors and wiring products for motorsport harnesses, EFI wiring and custom automotive electrical systems.

Shop Tefzel Wire Shop Raychem DR25 Shop Connectors

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FAQ

What materials do I need to build a motorsport wiring harness?

A typical motorsport harness uses Tefzel wire, DR25 sleeving, adhesive-lined heatshrink such as W5DL or ATUM, sealed connectors, terminals, splices, labels and proper documentation.

Why use Tefzel wire in a motorsport harness?

Tefzel wire is commonly used because it is compact, lightweight and suitable for professional wiring harness builds.

Do I need DR25 on every harness?

DR25 is commonly used for outer harness sleeving in motorsport and engine bay wiring, but the exact sleeving choice depends on the vehicle, environment and harness design.

Do I need adhesive-lined heatshrink?

Adhesive-lined heatshrink is useful for sealing, strain relief, repairs and transitions. DR25 protects the wire bundle, but it does not seal the ends by itself.

What connectors should I use for engine bay wiring?

Use connectors that suit the circuit current, wire size, pin count and environment. Deutsch DT, DTM and DTP connectors are common choices for sealed automotive and motorsport wiring.

Why is harness documentation important?

Documentation makes the harness easier to install, diagnose, repair and modify later. It should include pinouts, wire colours, wire sizes, connector names, fuse details and splice locations.

Last updated: June 2026

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