I have same problem. When i push to the brake my trailer abs comes on. After reading all these comments i checked my 40 amp wnd it looks like bad.
I am gonna change it soon. Hope it will work.
Volvo670, that should fix it. I had the same problem, blown 40 amp fuse, new one put in and it's been working since. That was last year. Mine was the big 40 amp blade fuse under the hood on the fire wall marked trailer auxiliary.