Inertia Switch

Inertia Switch - a full explanation

Background

An inertia switch has been incorporated into the electric fuel-pump circuit as an additional safety feature.

In the event of a sufficiently severe impact, the switch automatically cuts electrical power to the fuel pump, reducing the risk of continued fuel delivery following an accident.

Crash-activated fuel shut-off has been widely used on production cars, while positive fuel-pump isolation is also an important consideration in competition and track preparation. The switch was fitted particularly with the car's occasional track use in mind.

How do I know when the inertia switch has been activated?

When the fuel pump electrical supply is cut, the engine stops.  However, the engine could stop for any number of reasons, including the inertia switch being activated.

Hence, a flashing warning  LED light indicates on the main centre dashboard (the speedo) when the inertia switch has been activated.  The switch can be manually reset by pressing on the top; it is located on the LHS of the boot space.

There are two potential problems might arise:

1.  if the inertia switch is faulty and cannot be reset meaning that the fuel pump cannot be restarted and the engine will therefore not start;

2. if the flashing warning LED fails and does not indicate that the inertia switch has been activated meaning that the reason for the engine stopping is not apparent.

These two problems are overcome in the MM2000 with the simple circuit shown below, where is can be seen that:  

1.  An override switch on the small aluminium panel accessed through the hatch on the LHS of the boot allows the pump to operate, regardless of the state of the inertia switch.  An LED positioned adjacent to this switch illuminates when it is in the 'override' position to ensure that it cannot be left on unknowingly.

2. A push-button, mounted on the same aluminium panel permits a test of the function of the flashing warning LED on the dashboard.