I had a similar issue not to long ago with the ground that powers the solenoid. I also put a ground from the battery to the solenoid harness and the forklift started. The problem was that the ground wire on the other side of the harness was broken. Follow the power wire through the harness and you may find a break through. Mine was by spark plugs 2&3. Good luck

Check fuel relay, dual fuel switch , fuel fuse. Fuses. All at or below fuse box. Solenoid activates from ignition circuit for distributor. If dual fuel, there's a switch by vaporizer. Make sure your 2 wires to distributor are good. Check grounds by 3 &4 cylinder on block.