The 8,000 pulse per revolution signal generator for GM transmissions with speedo cable drives. If you plan on using an early Ford-O-Matic, please contact Classic Instruments for speedometer sending unit options. Early Ford-O-Matics have a specific speedometer cable connection that requires a separate special adapter. Also note that some Mopar transmissions do not have a speedometer cable output. If you plan on using a Mopar transmission, check the rear of the transmission for a speedometer cable connection where a standard sending unit will thread on. If none is present, please contact our tech department for other speedometer sender options.