It sounds like your travel trailer has an RV-style 7-way blade plug, such as what is shown in the linked photo. This is a popular configuration for trailers with electric brakes and 12V power service.
You can install a mating 7-way socket on your 1991 Volvo 240 Series to provide lighting, a brake signal as well as 12V power using our brake controller installation kit # ETBC7. The kit includes a 7-way vehicle socket, wiring, circuit breakers and everything you need for installation of a... view full answer...
I contacted Thule directly and they informed me that this is a rack that is only stocked in Asia. They encourage you to contact Thule Asia or the Thule website for the Philippines. view full answer...