Brake Test Diode

In this picture you can see the white/red on the left and the green/orange on the right, and the diode unit has a male spade on one side and a female on the other so it cannot be connected round the wrong way. Don't be tempted to connect the two wires together (you are physically able to) as it will simply cause the fault condition. The body of the unit has the circuit symbol for a diode indicating the direction of normal current flow (positive to negative).