Yes this is not uncommon…one day getting in to a Thomas Conventional school bus and experiencing a no start meaning no start crank along with an aggravating alarm going off in your ear. The rear emergency exit on Thomas C2 Conventional buses have a Vandalock system that will not allow the bus to start if the emergency exit door is locked. This is for safety if the bus is in an accident and the rear door is the only way out and you have hysterical school kids trying to figure out the lock on the door.
This starter interlock is a great idea to avoid this scenario but a pain when the Vandalock fails. Most times the problem is the door is locked or accidentally activated by the main latch which sometimes catches on the lower pin that slides towards the door latch to contact the circuit in the vandalock module which is screwed on the wall to the right of the latch. All that is required is to move the slider all the way to the left disengaging the Vandalock module.
This is the normal position but if that does not fix the problem the module might have failed. In this case that came true with an internal module problem that caused contact without help from the mechanical part of the latch. Two screws and a connector the problem was solved and down time was avoided considering we stock the module all of the time due to steady failures through out the years. It is easy to hear the details and know exactly where to go with troubleshooting.
When you first encounter this issue it’s mind boggling deciding where to start looking for the problem. Key on alarm on no starter action. If you remember that you will immediately know that it’s the Vandalock that is the cause. If the bus starts and you have an alarm it’s going to be either an emergency side window or one of the roof hatch alarms. All of the other buses in our fleet have this Vandalock at the rear emergency exit. Thomas Pusher buses have a side door alarm as well.
The International Conventional buses have an additional Vandalock above the entrance door key activated from the outside. It can trigger from the lever in the upper compartment losing contact with the vandalock switch sometimes because of the weight of the lever. If the bus is travelling on rough roads this can happen. Rule of thumb is to make sure all of the emergency exits are not locked before attempting to start the bus.