There is a whole thread on this somewhere. My advice to you is to get the fifth wheel rewired to a five prong. Without that, backing up is a nightmare. There is a metal "key" you can get that will allow you to back up without the brakes locking up, but then you have to get out, put the key in, get back in and try to back up. Hopefully, the key will not have fallen out, although it often does. I got so sick of the problem, that I took my Landcruiser to a trailer shop and had it rewired for $80.00. It was about the best $80 I've ever spent.