For your 1995 Volvo 850 I would recommend that you install a Tow Ready Wiring Harness Kit, part # 119177KIT, like the one you referenced. This product has a 5-way connector that would provide you with a reverse lockout solenoid circuit and would work well for you.
I attached installation instructions below for you to check out also. view full answer...
Although I'd love to sell you a hitch, the only ones available for your 1994 Volvo 850 are Class II rated, which has a maximum capacity of 3500 lbs, which is about 400-500 lbs less than your trailer will weigh. And not to add insult to injury, but my research indicates the towing capacity of the Volvo 850 is a max of 3300 lbs, which again is well under the weight of your horses and trailer.
For the safety of you, your horses and other motorists, I can't recommend using that vehicle to... view full answer...
I do have an option for you but there are no trunk mount bike rack options confirmed to fit a 1996 Volvo 850 Series. That said, you can install a trailer hitch, the Curt Trailer Hitch Receiver part # C12211 and then use a hitch mounted bike rack like the Swagman Trailhead 2 Bike Rack part # S63360. This will be a far better option in regards to ease of use. view full answer...
The Yakima LongArm Truck Bed Load Extender part # Y01149 is our best out of the box option for matching the roof line on a wagon as it can be adjusted to one of the following heights.
Low Bar Heights - 40 in, 37 in, 27 1/2 in, 14 1/4 in
Mid Bar Heights- 41 3/8 in, 38 1/4 in, 28 in, 15 1/4 in
High Bar Heights- 42 3/4 in, 39 1/2 in, 29 in, 15 3/4 in
If this won't work for you, your only other option would be to go with something like the Erickson Big Bed Junior Load Extender for Truck... view full answer...