Fuel gauge lights keep flashing mercedes benz s320 car has gas

Check coolant level . leaking fuel lines while running and stopped, gas tank filler cap , temperature censor ,low oil pressure , crank censor and fuel pump . Could also be the ECU ...

You may be overfilling and allowing excess gas go into canisters sensor "smells" excess fuel. Always stop at first bowser click-off and proceed slowly.

run the fault codes as you may have a problem with the canister system and purging of the system

Change gas cap.

You never leave a car running, as it will
overheat the Exhaust Converter
When you run out of fuel, you sometimes
ruin the Fuel Pump
It depends on gas to lubricate it,as strange as it sounds
Check fuel pressure & volume at the motor with a gauge

FUEL PRESSURE FOR S320 MERCEDES BENZ IS 46 - 52 PSI WITHOUT VACUUM APPLIED. 53 - 61 PSI WITH VACUUM APPLIED. 36 PSI RETENTION AFTER 30 MINUTES.

theres a couple of things to check for this first generation series,, check the Air flow meter connector FP terminals, and intake tube, make sure its tight and doesnt have a leak.

generally the light will quit in a weeks time
if not take it in to have the codes cleared to get the light off

Fuel level sensor is in the gas tank, may be faulty or just dirty, make sure to fill the tank entirely full with premium unleaded, ad a high quality fuel system cleaner / de-gunker, this may clean the sensor enough to feed back to the gauge. It could also be the fuel gauge itself, but that is less likely. Mercedes will be happier with at least 1/4 tank of fuel at all times, and don't skimp on low octane gas!
As for the check engine light, you may have a bad gas cap... believe it or not a gas cap that doesn't seal properly will throw the check engine light. If you get the codes read (for free) at an Autozone or similar parts store it will likely read "evap system" as the problem, which will likely end up being the gas cap.
Take your car to a service center that does a true "flush and fill" of your a/c system. Those little canisters will just waste your money, and they never truly clean and re-lubricate the system like a flush and fill will do.

you have a leak in the fuel evaporative emission system. The fuel light flashes when the gas tank and system is not sealed, and the purge control cant **** vacuum or hold vacuum in the tank. Usually its the gas cap not sealing the tank correctly, the "activated charcoal canister shut off valve" wont completely close the system, or the "purge control valve" under the hood isnt opening/pulsing correctly enough for the engine manifold vacuum to create the vacuum in the gas tank