TOYOTA - Mk3 Supra - Wiring Harness
Repair Only Full Harness
Difficulty(0-5): 3 5
Time: 2 hours 20-40 hours
Tool Specialty(0-5): Repair: 3 Full: 4
Cost: $5-150 $300-1,200

Tools Required:

  • Sockets: 10mm, 12mm
  • Wrenches: 12mm, 14mm
  • Specialty: Multimeter (AC Votls, DC Volts)
  • Specialty: Terminal Extractor
  • Specialty: Open Barrel Crimper 22-10 AWG
  • Specialty: Wire Stripper
  • Specialty: Wire Cutter
  • Here are some Amazon links hand selected by me for the exact parts I used in this project. Your purchases through these links help fund this site and keep new info coming:

PARTS REQUIRED (Full Harness):

  • Wire: ~1000'
  • Connectors: See table below
  • Terminals: See table below
  • Splices: Open Barrel
  • Heatshrink: 1/8"- 2"+
  • Wire Loom/Sheath: Various lengths/diameters
  • Wire Seals/Plugs: 070, 090
  • Here are some Amazon links hand selected by me for the exact parts I used in this project. Your purchases through these links help fund this site and keep new info coming:

  • Overview:

    Old wiring can cause all kinds of problems for mk3 Supra owners. CPS wiring goes bad for many people, but many other sensors can also suffer from wiring decay and make troubleshooting very difficult and time consuming. My wire harness was so bad I opted to build a brand new one. Here's a summary of dozens of hours of research and documentation. In exchange for a small piece of my sanity I can now provide the info below.
  • Terminology:

    Let's get on the same page. Wiring terms are confusing to new comers and if you don't have this understanding of the wiring system it will be tough to source components. Some of this may be obvious, some may not.
  • Wire (Insulation and Conductor)
    The wire is the conductor (usually tinned copper) that actually transmits the signal with insulation surrounding the conductor to contain the electrical signal. This is the most basic part and I'm sure you know what a "wire" is by now.
  • Terminal (contact):
    This is the metal piece that clamps onto the wire conductor and fits into a "connector" to allow you to plug a set of wires into another connector or a component like a sensor or the ECU.
  • Connector:
    This is the plastic piece that you physically touch when disconnecting wiring. There is usually a tab to click the connector into either another connector or a component. Connectors have numbered "positions" where terminals can be inserted. If you're building a new wire harness you better damn well learn your connector positions. Troubleshooting will be a nightmare if you don't get the connector positions correct.
  • Seal:
    Seals are used in most wire connectors that are not in the cabin. The seals are rubber pieces that are clamped onto terminals and help to keep moisture out of the connector.
  • Plug:
    A plug is used to block a connector position altogether. What happens when you have a 10 position connector and you only need 9 of those 10 positions? You put a plug in the position you're not using.
  • Splice:
    If you have a 3 way intersection of wires you'll need a splice. If you need to connect two wires permanently without a connector, you'll also need a splice.
  • Sheath/Loom:
    This is the material that covers the wiring harness wire sections and protects them from abrasion and heat.
  • Plug:
    A plug is used to block a connector position altogether. What happens when you have a 10 position connector and you only need 9 of those 10 positions? You put a plug in the position you're not using.