I guess I’m not exactly sure what you mean by lockout cap, so I assume yours is the same as mine.
You need to check and see that the 5th wire is working when in reverse, check all wires to the solenoid, I had the solenoid fail once on mine, the other time a wire came off the solenoid.
On the trailer tongue there should be a hole up top where you can put the a pin in to manually lock out the brakes from activating, I used the little locking pin from the trailer hitch, in short time I actually bent it a little, so I stopped by the hardware store and got a much more stout version and that works really nice, with the exception of a empty trailer the brake still seem to lock up even with the pin, and can make it a bear to backup up hill.
Assuming it’s a tiedown engineering trailer hitch components , more info can be found on their site. http://www.tiedown.com/amarinedls.html