280sl what's this box

on the bulkhead of my 28osl (70) is an electrical box with an arm connected to a rod and cable mechanism. I can't find where the cable goes to but when the arm is in the up position it seems to kill the power to the ignition circuit. Is this some kind of starter kill operated from inside the car for security. Is it original? I have also had the engine rebuilt and the fuel injection overhauled but am still struggling to get more than 10mpg, how do I achieve the average of 15mpg. Petrol is twice the price here in the UK that you pay so I have to have it running as economically as possible

[jgl1]

Should be the neutral safety switch, designed to prevent the engine from being started unless the trans is in park or neutral.

Fuel economy was never good on these vehicle, primarily due to the fuel injection system - these engines had a tendency to run rich. What does the engine oil look & smell like? Does it appear to be diluted by gasoline? If you're doing the work yourself, a factory service manual is an absolute necessity. Otherwise, you'll need to find someone highly experienced with the M130's setup.

Assuming that the rebuilds were done properly and the valve clearance and cam timing is correct, you need to ensure that every subsystem of the fuel injection is up to spec and adjusted properly. No computers here to pick up the slack and compensate for wear: this is all mechanical. Are the linkage rods properly adjusted and moving freely? Are the brass support bushings worn? Are the venturi body's butterfly plate and actuator arm set to specs? Is the plunger controlling the warm-up air bypass valve worn or sticking? Is the plunger depth properly adjusted? (It uses shims to achieve proper specs.) Inspect the air filter located at the rear of the injection pump - a clogged filter will enrichen the mixture. The cold start injection valve has a tendency to weep fuel as it wears - it almost certainly warrants replacement at this point if it is the original valve (and its not cheap). You may also wish to consider converting to electronic ignition - the hotter spark will help a bit with improving fuel economy. Stateside, Crane offers a good kit. E-mail if you need additional specifics. Good luck.