If you hook your trailer up and pull the brake slider all the way over, your trailer brakes should be locked up. If they are not, then you have a problem somewhere. Sorry to be so simplistic but there are a number of things that could be going wrong. I will try to describe the process I would go through if it were me.
Step 1 - first thing to check is make sure your trailer connector on both the trailer and the truck side don't have any mangled pins. If both connectors look physically intact, spray some contact cleaner into all the connector openings and plug the connectors in. Unplug, spray some more contact cleaner, plug 'em in again. That helps to clean the connector mating surfaces. Check all your running lights, turn signals, brake lights... If they are all working, chances are you do not have a connector problem, or a blown lighting fuse problem. Seven pins in that connector, if all your lights are working you've just eliminated four of them as having a problem. If you have no trailer lights, then your problem is going to be more complicated to diagnose.
Assuming everything but the brakes are working up to this point, the next thing to check is the fuse that drives the trailer brakes. Quick edit, thanks CRASH68 for posting this on another thread:
This should be the all the fuses for the trailer plug wiring and the ITBM:
F53 ATR 20 amp Left Trailer lights
F81 ATR 20 amp Right Trailer lights
F29 FFM 20 amp Trailer Park lights
F28 FFM 20 amp Trailer Back up lights
F30 FFM 30 amp Direct from battery
F11 J Case 30 amp Brake Lever <---------------------
F87 ATR 10 amp ITBM module
Pull that fuse out and install another one. I have seen blown fuses that look good right up to the point you put some current through them. Pinch the brake controller and see if the trailer brakes lock up. If they do, toss the old fuse and go have a beer. Any beer except for Corona. LOL If you still have no trailer brakes, put the old fuse in your glove compartment as a spare.
If you have trailer lights and no brakes then....
Step 2 - I would pull the pin on your breakaway cable and see if the trailer brakes lock. If they do, the problem is either in the connector or the truck side of the equation. If the brakes don't lock up, get a meter and check the voltage on your emergency brake battery on the trailer. It should read a solid 12 volts. If the battery is good, sounds like you have a wiring issue on the trailer itself.
If the battery is good and the trailer brakes lock up when you pull the breakaway pin, stick the pin back in and go to...
Step 3 - You probably need to take the truck/trailer to an RV center or the dealer at this point. If you have trailer lights but no brakes, good breakaway battery/switch, good fuses, then there's a big red arrow pointing at your brake controller.
IF you get to this point and you have NO trailer lighting and NO emergency breakaway brakes, then you have a trailer wiring problem. If the trailer manufacturer followed the standard color code, you're looking for a blue wire with an issue. Either broken somewhere between the tongue and brakes or shorted. If the brake wire is shorted, the brake controller should be telling you so, assuming it and the truck wiring are good.
It's hard to diagnose any further by remote control. Feel free to ask any questions on the above, I'll try to help as I can!
