Shown below is the MGA direct curcuitry. These circuits are not fused, presumably because a burned fuse would cause all of the lights to go out. The snap connectors labeled EC are located in the right rear corner of the engine bay. For the MGA 1600 the sidelamps are single filament bulbs.
NOTICE: The lighting switch is directly adjacent to the foglamp switch on the dash panel. The small red wire connecting lighting switch S1 terminal to the foglamp switch may have both ends extending from the same location on the wiring harness, along with three other red wires which connect to the lighting switch. Any time the harness has been completely disconnected from the dash, you may need to use a continuity tester to determine which two of these five red wires are common. One of those common red wire ends then needs to be connected to the foglamp switch.