On a Big Tex single-tire trailer with electric brakes, the lamp check and the brake check are two different tests. A trailer can pass every light and still fail the brake one. That verdict holds for the 1,500 to 21,000 GVWR single-tire trailers covered by the 2020 Big Tex owner's manual this procedure comes from. It stops holding in two cases: the trailer has no electric brakes, or the tow vehicle is not the compatible setup with an electric brake controller for that model. In either case the brake half of this check changes, and the tow-vehicle manual and the trailer's own manual take over.
Below, the route runs from the source of each command outward, and each later step closes something the earlier one leaves open.
Start the Check at the Tow Vehicle
Every command in this procedure starts in the cab. Electric brakes and lights on the trailer are controlled through the connection to the tow vehicle, generally a multi-pin electrical connector, which is why you set the tow vehicle up before you walk back and look at a lamp. Downstream of the switch sits the trailer. Until the tow vehicle sends a command, the trailer has nothing to show you, so a dark lamp tells you nothing until you know the command was sent.
Set the tow vehicle up deliberately: lighting circuits live, headlights on when you want tail lights, brake controller powered and connected. An unswitched control is a likelier explanation than a wiring fault, so spend the first minute on the controls rather than on the lamps. Before you read any result, look at the plug itself: a partly seated connector is its own false pass, because it can pass some functions and drop others and send you chasing the wrong end of the trailer.
Command Tail, Brake, and Turn Lights Separately
Turn on the tow vehicle headlights and watch the trailer tail lights. Have someone press the tow vehicle brake pedal while you watch the trailer brake lights. Then do the same for the turn signals. The manual treats these as three commands through one connector, and so should you: three results, not one event called the lights work.
Read the pass narrowly: the commanded lamp changes at the trailer while the tow-vehicle control is held, and it returns when the control is released. Tail lights coming on with the headlights prove the running-light circuit; the other two commands still owe you their own answers.
Two people make this straightforward: one holds the pedal or the stalk, one watches the trailer. Being alone and unable to hold a control and watch a lamp at the same time is a condition to solve before you start, not a step to skip. Be sure the lights and the brakes function properly before the trailer is towed, and treat any unverified command as an open item rather than a pass.
A Lit Lamp Is Not a Brake Test
A brake light proves the brake-light circuit. Nothing more. Power for the lighting circuits and, on a trailer with a separate braking system, power for the trailer brakes both travel through the connector, but brake power itself is sent by the tow vehicle's electric brake controller, which means the lamp you just watched answered a question about a filament and not about whether the controller's output reaches the trailer brakes or whether those brakes apply.
That is the false pass worth building your check around. Every lamp answers, the walk-around ends, and the brake circuit has still never been proven. The shortcut — all the lamps work, so the wiring must be fine — is the assumption that puts a loaded trailer on a highway with no trailer braking behind it. So the next check has to be the pull itself.
Confirm Brakes With a Controller Pull Under 5 mph
If your trailer has electric brakes, your tow vehicle has an electric brake controller that sends power to those brakes. Before towing on the road, you must operate the controller while trying to pull the trailer in order to confirm the electric brakes operate. Method, per the manual: while towing the trailer at less than 5 mph, manually operate the controller in the cab, and you should feel the trailer brakes operate.
Treat the pass condition as felt brake operation, not as a lamp and not as a controller display. If you feel nothing pulling against the tow vehicle, the check has not passed, whatever the lights are doing. That 5 mph figure is the manual's condition for this brake-confirmation step on this model, not a general speed limit and not a towing rating.
When Several Functions Fail, Suspect the Connector
The connector is the device that connects electrical power from the tow vehicle to the trailer, and it carries brake lights, running lights, turn signals and, if the trailer has a separate braking system, power to the brakes. Why one fault can show up as several failed checks comes down to shared routing: all of those functions use the same path, so one damaged pin or a plug that is not fully seated interrupts more than one circuit at once, while the lamps themselves fail independently of each other.
Which means the pattern matters more than any single failure. No brake lights together with no left turn signal points at the shared connection first; several unrelated bulbs giving up on the same afternoon is the less likely story. Where you look first is the useful output here, not what you replace, and the repair details belong to the model's own manual.
The Breakaway Battery Is a Separate Pass
If it is equipped with brakes, the trailer also has a breakaway brake system that can apply the brakes if the trailer comes loose from the hitch ball for any reason, and it comes with its own separate instructions. The system, including its battery, must be in good condition and properly rigged to be effective.
Why a controller pull cannot stand in for it comes down to which energy source is being tested. One pull proves the path from the tow vehicle's controller to the trailer brakes; the breakaway system has to work after the trailer has already separated from the tow vehicle, on its own stored energy, through its own rigging. Which means a pass on the pull leaves the breakaway battery and its rigging exactly as unproven as before.
Suppose a trailer sits for a season between jobs and gets pulled out for one Saturday haul. The pull can pass perfectly while the breakaway battery is flat or the rigging is tucked away where it could never pull; the two systems simply do not share the parts that would reveal it, so the breakaway condition needs its own look every time the trailer goes out.
Which Order Prevents a False Pass?
Run it in this order: cab controls first, the three light commands second, the brake controller pull third, the breakaway condition fourth. The sequence is not a ritual. It exists because each later step covers a different way the earlier one can be trusted too far. A lamp response does not prove brake apply, and brake apply through the controller does not prove the breakaway battery or its rigging. Which means the order keeps the checks from borrowing each other's evidence.
If you keep only one check, keep the brake controller pull with the trailer connected. It is the manual's brake-operating confirmation, and it is the one result no lamp can produce for you. Run it before the trailer leaves the lot, and run it again after any change of tow vehicle, controller or trailer.