Shown below is more of the MGA fused ignition circuit diagram. This page shows the brake light and turn signal circuits for the MGA 1500. This model uses just one filament in the rear lamps for both brake light and turn signal, so it incorporates a relay box to switch the bulb out of the brake light circuit and into the turn signal circuit when you operate the switch on the dash. Snap connectors labeled EC are in the engine compartment near the starter switch.