The electrical wiring was probably the most time consuming component of this project.
The electrical system was designed so that all of the functions of the Engine Control Module (ECM or computer) were fully operational. The design of the VN Commodore wiring was followed where possible, some changes were made to allow the car to be fuelled by both petrol and LPG.
I was lucky enough to get the entire body wiring loom out of a VN Commodore, as well as the wiring loom attached to all of the engine sensors and components.
I tried to design the wiring required for the new engine in a way that required as little modification to the existing HZ wiring as possible.
This was made a little easier by the way the original HZ wiring was designed. Most of the engine control signals were connected to the engine via three connectors located at the top centre of the firewall.
Engine bay wiring
I assembled an engine bay wiring loom that connected to the above three connectors, and then, via the necessary relays and fuses, connected to the factory VN Commodore engine wiring loom.
The above photograph shows the engine bay wiring loom. In the top left corner are the three connectors that interface to the original connectors in the top centre of the firewall. In the centre of the picture are three connectors that connect to the Commodore engine loom. At the bottom left corner are the relays and fuses that are mounted on the drivers side wheel arch.
The factory VN Commodore engine loom runs over the passenger side wheel arch, through a hole in the firewall and connects directly to the computer, located behind the passenger side kick panel.
The engine wiring loom design meant the battery had to be relocated to the drivers side of the engine bay. This also allowed the air box to be located in the old battery position. The windscreen washer tank and charcoal canister had to be moved to allow for battery relocation.
Under dash wiring loom
The under dash wiring loom connects between the computer, the transmission (via the transmission wiring loom), the park/neutral switch (at the base of the steering column), the original HZ fuse box, the speedometer and the Check Engine Light, which was fitted to the unused bottom right tell tale lampholder on the dash.
Also, part of this loom is the speedo electronics box (see Speedometer) and two relays required to condition the park/neutral and engine cranking signals required by the computer.
Transmission wiring loom
Another small loom connects to the Transmission speed sensor and to the torque converter lockup / 4th gear-overtemp connector.
Fuel guage interface
A VN Commodore fuel tank, electric pump and fuel level sender were fitted (see Other bits). An electronic interface had to be included to make the HZ fuel gauge compatible with the Commodore sender. A circuit diagram of the device I designed is included below.
The only other wiring, not shown on this page, is a single wire to power the in-tank fuel pump.