If your 1988 Coleman is the same as our 1986 was, there was never a provision for mounting a battery. However, our camper came with a 12V extension cord that plugged into the cigarette lighter on the tow vehicle on one end and a two pin connector on the other. The two pin connector was tied up with the trailer wiring harness but not part of the harness that plugs into the vehicle. It should have one black and one white wire running from the connector into the trailer. What we ended up doing was mounting a battery on the tongue and then connecting the battery to this two prong connector. As BigBaron mentioned, don't forget an inline fuse. I also read in another thread where you are asking about charging the battery through shore power. Our camper had the original converter and was not able to charge the battery when connected to shore power. It had a switch on it that allowed you to select 12V/Off/120V. If your converter is original, the only way to charge the battery would be to take a battery charger and connect it through normal methods. If you have any problems locating the wires, send me a PM and I'll email you the pages from the owner's manual.