It’s been awhile, but I’m confident that there isn’t a ground between the Leopard electrical system and the chassis. Even if there is no continuity between the engine and chassis, the chassis has four insulators called tires. The ground is only relevant to the circuit it’s a part of. For instance, if you apply 12 volts to the starter, nothing will happen until a return path, the ground, is established back to the battery. I have never tried this, but in theory, you should be able to have continuity between the engine and the negative battery lead. I’d remove the leads from the battery before trying this and this might not work if the control box is switching the ground and not the positive to the starter. Better yet, if someone has tried this, maybe they will post their results.
When I connected the ground, I always used a star washer between the ground lug and the engine.
Haven’t seen Jim Russell on the forum for a long time now. Maybe if he’s monitoring the Forum, he could point you in the right direction. Or, and the better way, you call Russell Karting. The following link is to the site and click on the contract page.