The ignition interlock system on school buses is to make sure that the bus will not start if the emergency exits are locked. This is accomplished by two separate circuits wired in series, the first is the ignition interlock that prohibits the starter from engaging; the second is a buzzer that notifies the driver at the driver seat and at the door that has triggered the interlock that a door is locked.
This is to allow access for emergency personnel should there be a need to gain entry from the outside.
The easy way to start this process is:
1) Look under your dash at your key ignition switch, there will be a #10 wire it will be black or purple, there will be a smaller wire the same color with a tracer color.
2) open the door to your wiring panel and find those two wires coming in from the front of the bus, this is a large bundle of wires so you may need to remove a couple of ty wraps to find these wires.
3) Trace these wires, the biggest wire will go to a terminal and be fasted with a nut, the smaller wire will go to a relay, either directly or be spliced to a different color wire.
4) Trace the smaller wire to the relay, the relay will have one yellow wire which provides a ground to the relay to allow the starter to work, there will be a jumper wire from one terminal to another and that will have a wire that will lead back to the terminal where the #10 wire is connected, it most likely will be the one above or below the #10 wire
5) Disconnect the wire from the terminal that comes from the relay.
6) Cut the wire going to the relay and crimp a ring terminal to it.
(this is the smaller wire from the key ignition)
7) Connect this new ring connector to the terminal you just removed the wire from the relay.
Test your engine and it will start.
9) Unscrew the relay and disconnect the yellow wire, save the relay in your parts box, these are common use items.
The buzzer works opposite of the interlock, it will activate when it finds a ground, where the interlock looks for a continuous circuit.
1) Find the buzzer, it is right next to the relay you just removed.
2) Remove the power wire from the push on terminal strip just above it.
3) Remove the wires from the other terminal on the buzzer.
4) Unscrew the buzzer
5) Start bus and notice no annoying buzzer
Once you have removed the relay and the buzzer make sure you pull the wires you disconnected from the buzzer and the relay out of the way maybe put a crimp cap on them or tape the ends to keep them from touching something they should not, then ty wrap them and the big bundle of wires you opened up to find your ignition wires.
Below are some pictures, and a picture of the schematic that is on the door to my engine.
This worked just fine for me, and I believe it is better than trying to disable the interlock at each of the door locations and the buzzer trip points.