While a gasoline engine is an array of fuel lines, exhaust pipes, coolant hoses and intake manifold, much akin to a plumbing system, an electric vehicle is a complex connection of wires. Under the hood, there are a lot of differences between the two.

The gasoline engine is replaced by an electric motor, the electric motor gets its power from a controller and the controller gets its power from an array of rechargeable batteries rather than from gasoline in a fuel tank.

More precisely, the controller takes power from the batteries and delivers it to the motor. The accelerator pedal hooks to a pair of variable resistors that provide a signal to the controller indicating how much power it needs to supply to the electric motor.

There are two of these resistors for safety.(The controller reads both resistors and will not operate unless both signals are equal). For illustration, if the accelerator is pushed halfway down, the controller reads that setting and rapidly switches the power to the motor on and off so that it is on half the time and off half the time. 

Accordingly, at whatever increment the accelerator is pushed down, the ratio of the pulsing is determined. Since the "fuel" of an electric car is electricity, the electricity has to be stored in re-chargeable batteries to make it "portable" and available to power the vehicle. Electrical systems can be either DC power, which is more common due to greater simplicity and lower cost, or AC power.

Due to concerns about driving range and battery capacity, many people are drawn to a hybrid of gasoline and electric car technologies. A vehicle powered by a hybrid system entails more technological complexity, of course.

Quite simply, converting a gasoline powered vehicle to an electrically powered one first involves "ripping out the plumbing". This includes removing the engine, transmission, gas tank and exhaust system and then replacing it with an electric motor, controller and battery array as described above. Creating a hybrid system is more complex because of the requirement for both gasoline and electrical components.

Some forward thinking companies are making conversion kits that put everything required for a conversion into one neat package for motivated consumers. These companies have developed "custom" conversion kits designed to convert a specific conventional car model as well as "universal" conversion kits for vehicles for which no "custom" kit is available yet. If one does not have the expertise, more and more people who do have it are becoming available for hire.