Every once in a while we run into a solenoid a bit different from the common 3 post. The ground activated solenoid can be confusing if you are not sure how it is to be connected. These are common in old Ford tractor applications, such as our 6650-1023 used on 2N, 8N, and 9N series tractors. Most 3 post solenoids have their base or mounting grounded, so when a signal comes from the start switch, it flows through the coil pulling in the contact, and continues to ground through the solenoid mount.
Ground activated switches are a bit different in that the switch coil is internally connected to the BAT post. This means one end of the coil is always powered and the other end is connected internally to the solenoid switch post. When a ground signal is given to the switch post, the current can flow through the coil, pulling in the contact. The ground signal to the switch post is usually accomplished with a physical button switch, similar to the Ford tractor style shown below. *Note that most of the old Ford tractor applications were 6V and Positive Ground, meaning the positive post of the battery serves as the ground and the negative post of the battery is the feed for the system.*
*This is a basic wiring guide and will not cover every application or scenario. Always use caution when modifying a system. While Smith Co Electric deems this information accurate, we are not liable for problems arising from use of this information.