This 3 POST Motor Solenoid works with ALL Meyer plow pumps, and numerous other brands. It includes 2 mounting screws. Works with ALL Meyer hydraulic units except E-73 and Home Plow. Click on Related Products tab for OEM 4 POST version. We DO OUR BEST to keep this 3 POST in stock, but sometimes we have to substitute an upgraded 4 post, the one with 2 small posts marked S and I. The small white trigger wire goes to the S terminal, and the I terminal must be grounded. We include a jumper wire to ground the 4 post when replacing a 3 post. See pictures. IF YOU HAVE A 4 POST NOW, YOU CAN USE A 3 POST, IT DOES NOT NEED TO BE GROUNDED WITH A JUMPER. JUST HOOK UP THE WHITE WIRE AND OFF YOU GO. IF the solenoid is marked BAT on one side then the battery cable MUST BE connected there, not the load.