I am also rebuilding an old 1977 Marketeer. I have an HMK model 438 with overdrive. The overdrive is not on any wiring diagrams so I have my hands full. It is a fun project tho - I have restored an old club car and outfitted it with a solar panel so I never have to recharge it and I drive it to work and back everyday. I am replacing all the old solenoids and diodes as it had a couple of bad ones and tended to start with a jerk and go right to full speed when the pedal was half way down! Anyway, I recommend solar panels as a way to keep the batteries in good shape. Good luck on your project cart!