I've attached a photo here for reference for those who want to see a picture. If you notice the silver stripe on the diode, it's oriented towards the light blue wire, and away from the dark blue wire with the white stripe. Not every vehicle may have the same coloring of these two wires, but the diagram in the Alltrax XCT booklet will reflect the correct wire color for each specific vehicle. I have to deal with customers quite often who are totally confused when installing their solenoids so I'll try and explain how a solenoid works.
Typical golf car solenoids have four terminals. Two coil terminals and two contactor terminals. The coil terminals are the small ones and the contactor terminals are the large ones. When you provide 48 Volts of power to the two coils terminals, the solenoid will click (or close) and will make an internal connection between the large contactor terminals. As with any DC circuit, the solenoid requires a positive and a negative. The coil suppression diode is installed between the positive and negative terminals on the solenoid coil to prolong the life of the solenoid driver in the controller and the life of the solenoid itself. When the power is applied to the coils, it comes in as a sudden inrush of power. The coil suppression diode helps to protect the solenoid and the controller against voltage spikes during this sudden inrush of electrical current. A diode is designed to allow electricity to only flow in one direction. If the diode is installed in the incorrect direction, power can flow from one terminal to the other and end up in places it shouldn't be, creating a direct short between these two terminals. With a controller such as the Alltrax SR or the XCT, this is not going to cause any damage because it has built-in polarity protection. If you install a diode incorrectly on a solenoid with a factory Curtis controller, it'll ruin the controller immediately when you try to operate the car. It will fry the solenoid driver circuit. It's extremely important to install these diodes correctly the first time.
There is no polarity of a solenoid. The polarity comes from the diode. Lots of my customers are often confused by the fact that the light blue wire may have been on the right side of the solenoid, but is shown in the drawing on the left side of the solenoid. There is no left or right on a solenoid. It makes no difference which small post you use as long as the diode is oriented properly. The same can be said for the two large terminals. The Regen Diode that comes with the controller must be installed on the large terminals with the banded (striped) side of the diode oriented towards the side of the solenoid (left or right, it doesn't matter) where the incoming power from the battery pack is connected to the solenoid.
If you'll notice in the picture, the diodes that we use are not only marked by a stripe, but to make it even easier, there is a red side and a black side if you look at the wire on each side. Red being positive and black being negative. The Regen diode provided by Alltrax is the same way.
Sent from my iPhone using Tapatalk