1995 Mercedes s320 wont start, I think it has something to do with the Alarm System and or electrical system. the Battery is fine,

Some Mercedes models have two batteries. If you were not the original owner you may not know this. Why two. The extra battery operates the starter even if the main battery goes dead. The extra battery is usually located under the cabin filter in the engine compartment. It is a special battery (small) like a motor cycle battery. It has probably died. Check your owners manual as locations may have changed. It is about 100 fix if you change it yourself.

their are some electrical issues with s320 throttle valve electric failure --coil pack failure -- check fuses and relays then check battery and connections and try to start with boost if starts check and test battery and alternator --and check the wiring connections for loose , frayed , damaged ,and corrosion the following link are some of the problems acossiated with your vehicle
Newest Problem Reports for the 1999 Mercedes Benz S320

did you check the alarm system

Does the car start in Neutral? If it does then Park sensor switch is cactus.
Not sure of the fix but my S320 does this, sometimes starting OK in Park, sometimes not.

Could be a couple of things, if the motor turns over, you may not be getting fuel or fire, have the fuel pump relay looked at, if it needs fuel and the coil pack if it needs fire, that's where I'd start looking first. The last and most expensive component is the main computer itself

It dies after start since not having fuel. There are several factors needed to be checked:
1-Fuel injectors got clogged up or injector module control is having a problem.
2- Not having correct fuel pressure due to fuel filter gets clogged up.
3- Fuel pump is weak not delivering correct rate per spec.

Isn't there botton somewere on the door or left lower conner of dashboard to open trank remotely?

radio ask for code

I have the same problem on a s320 cdi, gearbox goes into limp mode and wont rev above or kickdown, at the 1st chance i get to stop i put into park or neutral gear turn off the engine and re-start and then everthing is fine, I read that if you put a new battery on it may solve the problem, it's something to do with the voltage dropping below 10.4 volts. Then it sends a message to e.c.u. that puts your gearbox into limp mode. Hope this will work for you. MERKY

you have a short. maybe in your alarm unit itself try to locate the control box for the alarm and unplug the starter kill relay and bypass it then try starting the car.