Get yourself a meter. Put it on ohms and connect one lead to a chassis ground. Take the other lead and start probing each battery cable. Each cable that shows 0 or very little resistance is a ground. Put in your chassis(start) battery and connect the negative post to one for the ground wires. Now take and connect one of the biggest cables left over to the positive terminal and try to start the engine. If it starts then that is your chassis positive, label them. If not try another cable. When you find them all(house and chassis) label them.