What would cause emergency light system in residential building to fail

According to an LG installation manual for the LMU540HV, if the flashing light is viewed on the indoor unit with the ceiling cassette light on the far right flashing 5 times, it is an error code meaning there is a communication error between indoor and outdoor units. I would start by making all indoor and the outdoor units have power. I would especially check to see that fuses or circuit breakers to the outdoor unit have not failed. Or check the outside disconnect to make sure it is working. Check with a volt meter to be sure you have 220 volts present to the outdoor unit. Also, if the 4 indoor units have emergency power off switches, make sure all 4 are turned on. Checking to see power is present both indoors and outdoors a good place to start. It the outdoor unit has power, there may be a relay that has failed or a power circuit board has failed that would cause it not to communicate.

pushing the emerg button will simulate a power failure and your light fixture switch to emergency built in emergency power pack.

could be that the battery that runs it is bad or gone down. something has failed in the system.

Only get a vacuum leak, if the booster check valve
failed & may effect the idle,not sure if it would be enough
to stall out the motor
What is the emergency switch? Parking Brake warning light?
That wouldn't have any effect on the engine idle

the parking lights and the other lights are different eliments inside the same bulb

CODE P1406 - EGR VALVE PINTLE POSITION CIRCUIT MALFUNCTION CONDITIONS. POSSIBLE CAUSES EGR SOLENOID VALVE IS BINDING OR STICKING. EGR SOLENOID CONTROL CIRCUIT IS OPEN SHORTED TO GROUND OR TO B+. EGR SOLENOID POWER CIRCUIT IS OPEN CHECK THE ECS 10AMP FUSE.EGR SOLENOID FAILED. PCM HAS FAILED.

Yeah, I have seen tons of these units fail early. Usually someone stripped the gears.
Another approach, in terms of lighting control, is use dusk to dawn or timed motion sensors. They are always "on time" where the clock needs to be changed many times over the course of season changes, etc. They do not need to be reset after power failure or daylight savings, they just always work/
In a commercial building, interior lights should be on 24/7 OR motion sensors, and external lights Dusk to dawn.
In residential, motion with duration timer systems seem to work the best. Replace the Intermatic. Even the digital Intermatic requires user intervention all the time.

Bad brake master cylinder could cause this, It will start leaking internally and not build up pressure. Will happen just do to age, will need to replace it and bleed brake system.

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The booster uses vacumn to assist your foot pressure. A leaky seal or diaphragm in the booster or a bad hose from the engine to the booster will cause the pedal to drop as it loses power assist. I think the brake light switch is mounted under the dash by the brake pedal. Fix the booster now, it may save your life.

Suspect faulty flasher relay. Relay is somewhat like an "On/Off" switch. If it fails, it will stick ON or OFF..in your cause it is ON allowing the hazard lamps to work continuosly without enabling the hazard switch. If the relay is tested good then replace hazard switch.