i dont think we need engineers cert here in perth???
the following is straight from WA Transport
Modifications that don't require approval
Many minor vehicle modifications can be carried out without specific approval, as long as they comply with the applicable legislation. Modifications that don’t require approval include:
Additional lighting
Air conditioners
Air shock absorbers
Alarm systems
Badge bars
Body markings and speed striping
Gearbox (pre 1976)
Mesh stone shields for wind screens and lamps
Mud spats and pebble guards
Optional manufacturer seating
Radio and stereo systems
Rear-view mirrors
Roof racks
Seat belts for pre 1969 cars (no full harness types)
Single tone air horns
Stabiliser bars
Sunvisors
Torque rods and traction bars (not semi-tramp types)
Tyre size and aspect ratio
Venetian blinds and other internal screening systems are allowed, subject to a clear view to the rear.
What to do if your proposed modification is not on the list
A list of modification that do require approval, and how to apply, is provided below.
If what you want to do is not on this list, or you are unsure, contact us. By contacting us first, you will ensure that:
The modified vehicle will be safe.
The vehicle's insurance remains valid
You avoid the inconvenience and expense of removing a vehicle compliance notice (yellow sticker)
You don't waste time and money on a project that subsequently proves to be illegal
Please note, if you modify your vehicle without the necessary approval you may be issued with a compliance notice (yellow sticker) and void your vehicle insurance.
Modifications requiring approval - limitations and conditions
For information on the following modifications please refer to the Department of Infrastructure, Transport, Regional Development and Local Government's Vehicle Standards Bulletin: National Code of Practice for Light Vehicle Construction and Modification (VSB14):
Alternative power
Body modifications
Brakes*
Electric drive
Engines
Fuel systems
Motorcycles
Seating and occy protection
Suspension and steering
Test procedures
Transmissions
Trike guidelines
*Note: Modifications to the braking system of a motor vehicle are permissible only where listed by the vehicle manufacturer as an option for the particular model. However, the fitting of a suitable power booster unit to a brake system is in order where it is an option listed by the vehicle manufacturer or is recommended by a qualified brake specialist. Passenger vehicles and their derivatives manufactured to comply with ADR 31 - Hydraulic Braking Systems, and ADR 35 - Commercial Vehicle Braking Systems, must not be modified without prior written approval from the department.