Trailer wiring SNAFU

[TPCDrafting]

So, the other night I'm hauling home 5 ton of hay for the ponies. Just toodling along at 65. I'm pulling a 24ft GN flatbed. I start climbing a hill and with the ol Cummins I just add a little weight to the go pedal and it's holding. All the sudden I lose power in 5th. It seems strange so I grab 4th. Still losing power, I'm checking gauges and all seems well. I'm down to 3rd and still losing speed. There happens to be an off ramp so I take it. Once stopped I figure out that it's the trailer brakes holding me back. They are on about where I had them set, not locked. So I drag this thing into a parking lot where I can have some light. I pulled apart the wireing plug on the trailer to find 2 wires have come loose. So I put them back in and all seems fine. So I head back for the interstate and as soon as I let off the brakes making the turn onto the on ramp the trailer brakes lock up. This time they are on hard! I can't move the thing at all. It's a quiet on ramp and it's now about 11:30 pm! So I jumped out and pulled the plug again making sure I did it right. Well one of the wires just frayed when I put it back together the last time. So I cleaned it up and maticulously put it back together. Jump in the truck and it will roll! Only now I have no trailer brakes and no running lights. WTF There wasn't many people on the road so I limped home. I returned the trailer to its owner the next day with the same condition. We hooked it to his pickup and it all works fine. So it's somewhere on the truck! When I got home I hooked my truck to my horse trailer and I get the same results: turn signals are fine, brake lights are FINE, but no running lights and no brakes on the trailer. Everything on the truck works fine with or w/o the trailer. I've checked fuses once and didn't find any burnt. I'll double check, but wouldn't the lights be out on the truck as well if the fuse was burnt? I know the brake unit is getting juice. It's a Drawtite somethin or other. It has a digital number readout when the brakes are working. You can set them to a number aka 2.5, 3.0, 3.5, etc. for how strong the trailer brakes need to be. When nothing is hooked to the truck all I get is a "." (period). This is normal when nothing is hooked up and that's all I get now trailer or not. So I know it's getting juice, but its not functioning. I don't get it, if the brake lights are working and the box is getting juice, it should work right? Sorry so long, any ideas???