Pull out your manual and find the appropriate page for the electrical system. Draw your own sketch of the components which are part of the starting circuit. This will allow you to identify the places where the starter system may be faulty. For instance you will probably find that the gear position switch down on the engine has to be in neutral in order to send a signal to the computer that allows the starter to activate. Once you have a rough idea of where the wires and components are, then do the same for the rear brake electrical components. You should find a common place in the two circuits which may be the faulty area. I suspect that a short is occurring at that common place either due to damage, corrosion or moisture.