If you are using a factory harness and are after an easy ECU upgrade, take a look at Haltech Plug 'n' Play Adapter Kits. These adapters plug directly into your Haltech ECU and have a set of factory connectors on the other side which plug straight into the factory harness.
A simple Haltech Plug 'n' Play product that allows you to be up and running in just a few hours.
The quick start guide will walk you through installation of the Haltech Plug 'n' Play adapter into your vehicle.

Suits: Plug 'n' Play replacement of the factory ECU for Toyota Mark II/Cresta/Chaser JZX100 1JZ-GTE VVT-I (JDM) Soarer (MY96-01) JZZ30 1JZ-GTE VVT-I (JDM) Manual transmissions only.

Includes: Injection molded plastic plug 'n' play adaptor harness, M14 x 1.5 air Temperature Sensor with matching plug and pins, auxiliary I/O 16 Pin Tyco plug and pins.

Notes: Installation of this Haltech product will prevent the factory TRC and ETCS systems from operating. Warning lights will illuminate on the dash cluster to indicate these systems are disabled. Removal of the TRC and ETCS warning bulbs from the dash cluster is recommended.