S250

I have an S250. Turn the key on, only the parking brake light goes on. Wait 10 seconds then the fuel gauge comes on and the temp gauge starts moving. Now you can start the engine, and operate the machine. If the fuel gauge doesent move there is no engine crank. If you wait ten minutes or so when you turn the key on all the lights in the right panel come on and stay on, even after starting the engine. Power going into the key switch (red wire) is battery voltage. When I turn the key on it drops to 8 or 9 volts. Same voltage coming out of the key switch (white Wire). Hour meter never comes on so I cant get any error messages or codes. What should I look for before getting raped by the dealer?