Wiring of the Vortec really is very simple, once you focus on the important components and circuits. The following describes general features of the 1996 model year engine. Newer engines are slightly different, but the principles are the same.
The most important aspect of the wiring is the connector that provides the interface between the Vortec electronics and the Land Cruiser. That connector is called C100. It is located in the main trunk of the Vortec harness, about 1' away from the VCM and the Fuse and Relay Center. The connections on C1000 are shown on page 8A-202-1) of the electronics service manual. You should become very familiar with it.
Basically to Run the engine you need to supply 12 volts of fused power from the 3mm red wire at A8 on C100 (circuit #142) to the ignition feed, E2 on C100 (circuit 3). You could alternatively use the 5mm E3 (342) as the hot wire. (this is how I did it) The power is supplied from the battery to the ignition switch with either A8 or E1 (any one of the 5mm hot wires). As shown on page 8A-10-1 to 10-3, the important circuits are A (run) and C (crank). Power supplied to E2 either by an ignition switch (run) or by simply jumping A8 and E2 will provide spark to the engine.
To crank the engine (run the starter), you simply supply 12 volts to E1, the starter relay feed, CKT #5). On page 8A-10-1 follow the 3mm yellow wire (CKT 5) from the start position down to below the triangles with A, B and C in them. The book then tells you to see the "starter and Charging Section on page 8A-30-0. Here
you can see that the starter is run by connecting the circuit involving the battery, the fuse and relay center, the ignition switch and the starter. At C100, you can basically run the starter motor by simply providing power to E1. Note, however,
that there is a side circuit that must be completed for the starter to run. That circuit involves the Park-Neutral switch on the transmission. When the start key is turned on, power flows thru C100 along the yellow #5 wire to the P/N switch. If the switch is in P or N the power goes through CKT # 1035, a purple wire to the starter relay in the Fuse/Relay center and then to the starter. The P/N position switch is located on the transmission. The purple wire (#1035) therefore runs through the branch of the harness running from the transmission to the B9
connector pin on the Starter Relay.
If the engine was originally mated to an automatic transmission AND you are retaining that transmission, you should not have to worry about the P/N switch (assuming the tranny is plugged into the harness). If, however, you are switching to a manual transmission, you will need to permanently jump the wireson either side of the P/N switch.
On the right of Page 8A-30-0 you should also note the charging requirements. Note that the diagram for the generator says to see page 8A-30-1. On this page you can see that the generator forms a circuit between the battery and the dash panel. You should notice that the generator will only work if the circuit is
complete. This means that you need to have the resistance in the circuit corresponding to the "Charge Indicator Lamp". I learned the hard way that the generator will not work unless you wire in a charge indicator lamp. This is really easy to do. Note that you simply run a wire to an instrument panel bulb (I used my 4WD indicator lamp) from the C3 pin on the C100 connector. Piece of cake.