Most factory wired CCars utilize a system of contactors to control motor speed and direction. A series/parallel contactor and a bypass relay control speed while a taller forward/reverse contactor handles more direction and a safety "neutral" position. These contactors control all the power to the motor and, even worse, must do this by opening and closing mechanical contacts under load. Motor current can be in excess of several hundred amps during locked rotor (another way of saying the motor is not turning yet). In order to minimize arcing/sparking at the contacts the contactors are energized sufficiently to slam the contacts into place.
If the contactors are operating on low voltage, rather than slamming into position they may slide slowly into position allowing plenty of time for the arcing of high current. This long duration if arcing causes a significant amount of heat buildup and damage to the contacts. Each time a long duration arc occurs small bits of the contacts are blown or melted away causing a buildup of non-conductive carbon... which only compounds the problem!
Well, CCars have a ton of connections, wire and switches that are all potential sources of D.C. power Loss. Each of these poor connections by itself only causes minor voltage drops sometimes only tenths of a volt. Start adding up all those tenths together and suddenly you have whole volts of power potential being lost! One new problem that has started showing up is a much more serious problem... the key switch in a CCar. Almost all power for everything in your car is controlled by this switch. With all that power going through such tiny contacts, arcing and sparking on occasion, the switch contacts get warm (or hot), start to corrode and in some instances start to melt. We have found some key switches dropping in excess of 3-4 volts under minor loads and contactors tend to be very big loads!
This article is still being edited and added to and is only here for reference....