Hello! I'm actively shopping for used a used popup. I have a 4 Pin Connector on my vehicle and want to be ready to fetch a trailer having a 7 Pin connector, without needing to first have 7-pin connector installed. (Some I'm looking at are 7, some are 4). What are the options for 7-pin to 4-pin adaptors, and where the heck do I get one? TIA!