Date registered: Dec 2012
Vehicle: 2003 S430
Location: Georgia, USA
Mentioned: 91 Post(s)
Quoted: 375 Post(s)
Wow! Quite a bargain, if that was not a typo!
I am somewhat confused by your post. There are three SAM (Signal Acquisition Module) units in the 2003 S430. Left, located at the left rear of the engine compartment; Right, located at the right rear of the engine compartment, and Rear, located under the right side of the rear seat cushion.
The Primary Fuses are located in two areas; behind the trunk lining forward of the battery, and under an aluminum cover on the front passenger's toe-board under the carpet.
Unless the owner had the key and the "ignition switch" (which is usually called the EIS, and is a very expensive electronic box) replaced by a dealer ($$$), that doesn't usually work. There are four units in the car - key, EIS, ECU and shifter - that are known as theft sensitive units. These are each hard-programmed with the car's identity, and cannot be individually changed. The best that an owner or an independent garage can do is to replace all four units with four matched units from a donor car, giving your car a new identity (and creating problems with door and trunk locks).
The only really effective "scanner" for the W220 is SDS (STAR Diagnostic System). You can buy a Chinese clone of the $15,000 dealer SDS for $450-600. If that is what you have, things will be better - not easy, but better.
There are many folks on here who are willing and able to help you. Your part will be to give us verbose, detailed descriptions of what you find, using proper terminology, and with photos if possible.