For the emergency door interlock:
I have a book of wiring diagrams for older Thomas conventional buses (which are wired similar to other Thomas buses). In 1995 they changed a lot of wiring stuff, but the pre-95 circuit diagram gives me an idea of how your switches were set up. My scanner isn't working right now, so I'll try to explain how it's laid out. Wiring colors may be different (your black and white wires should be yellow and dark blue according to my book, so it may vary by different models).
There are 2 switches at each emergency door with a Vandalock. One is just for the buzzer when the door handle is opened, that should have two wires. The other is for the buzzer and starter interlock when the door is locked, which should be the 4 wire one. It's a double-pole single-throw switch. One pole is normally open, the other is normally closed.
In addition, buses with a locking compartment over the driver's window for safety equipment storage may be equipped with an interlock. This will use a 4-terminal DPST switch just like the Vandalocks.
The buzzer circuit uses ground-side switching. There is power to the buzzer whenever the key is on. When any door is either opened or locked, the the respective switch grounds the wire from the buzzer. (The buzzer wire is connected to the normally-open SP door switch and to the normally-open side of the DP lock switch.)
The interlock is also wired with ground-side switching. The interlock uses an extra starter relay, fed by the ignition. The ground wire for this passes through each interlock switch, on the normally-closed pole of the double-pole switch. When each door is unlocked, the relay is grounded. When any door is locked, the ground circuit is broken.
Now that I've explained how it works, there are a few ways to disable it. If you can locate the interlock relay by tracing the starter circuit wires, you can simply connect the two wires (in the diagram they're shown as black wires). If it's easier to do at the side door (or rear door - make sure it's the closest one to the front of the bus), the diagram suggests that the interlock circuit is a yellow wire connected to the furthest terminals from the plunger. (On the overhead locking compartment, it will be connected to the terminals closest to the plunger.) Either connect these two wires, or ground the one coming from the switch cabinet (will be hot when the key is turned to start). I would suggest either bypassing the relay, or tracing the interlock wire and grounding it behind the switch panel, so you won't have a hot wire running the length of the bus.
The buzzer wire is supposedly dark blue, connected to the other terminals. One side will be hot when the key is on or in accessory, and grounding it will sound the buzzer. If you remove the buzzer or its fuse, you'll just have a dead wire running the length of the bus. (If you have the optional emergency door pilot light, it's wired in parallel with the buzzer - either disconnect the light with the buzzer or remove the fuse to kill the circuit). This circuit also runs to other non-locking exits such as pushout windows and roof hatches, which ground it through SP switches in the same way.
On newer buses (95 and newer according to my book), they used a different Vandalock design that would lock the handle by inserting a pin. To line it up, you would have to slightly open the handle, just enough to sound the buzzer but not open the door. These use only one switch, wired the same as the lock switch on older buses - double-pole, with the normally-open side for the buzzer ground and the normally-closed side for the starter relay ground. You should be able to disable it the same way. The diagram suggests newer models use a standard 5-prong relay for the interlock, and if you just connect the wires from the 30 and 87 prongs it should bypass the interlock circuit. Either that, or ground the yellow wire (circuit #32) from terminal 86, or at the door if you prefer.
Sorry for the long post, but hopefully this will help some future Thomas converters.
Thanks for sharing
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