check for power at the trailer connector.
Are you getting power to sockets? Make sure you have a good ground circuit
Take a light tester and check the pins at the truck side trailer plug. With the truck set for running lights check for power at the pins. If there is power then there is a loose or bad wire on the trailer side. If there is no power then there is a power problem on the truck side.
The center pin of a seven blade trailer plug is for reverse lights, not power. What type of truck is it? What trailer plug do you have...
First understand the wiring. It can use four to seven wires to control lighting. Choose the correct connector. Connect all the necessary components to work simultaneously such as electric trailer brake controller, backup lights and a 12V power supply. Take the vehicle to an expert if the task is tricky.
Change the trailer light bulbs to 24 volts and supply a 24 volt source to power them, in that order.
Primary brakes are situated at the front wheels and provide about 70% of a vehicle's braking power. Your secondary brakes are located at the rear wheels and only provide about 30% of a vehicle's braking power.
When you turn in a tractor trailer (or any vehicle with a trailer), the tyres of that trailer aren't going to take the same course as the tyres on the power unit - they'll go within the turn radius of the power unit. Drivers need to be aware of this, as this can cause the trailer to hit things the power unit would clear, such as curbs, utility poles, etc.
If you have a 1998 or newer it could be a fuse in the power distribution center under the hood. The whole trailer light system is fused through there.
The Control Unit and Harness are strongly recommended if you are going to tow anything that requires lights/brake controls. FYI, you don't have to get HONDA control units, most businesses that sell trailers sell various name brands and can do the wiring for you. Anyway, the wiring for the taillights and brakes lights of the vehicle are not strong enough to carry enough power to supply the electrical on a trailer (very dim-could cause a short). The Harness connects a power source (battery) to the trailer wires. The Control Unit is connected to the vehicle wiring as well as the Harness. When you step on the brake pedal, the Control Unit senses it and allows the power to go to the proper wiring on the trailer directly from the power source, therefore you will have brighter lights on the trailer. The same for parking and turn indicators. This is worth the money. I have this set up on my 2003 Odyssey.
Make sure that the wiring harness is properly grounded. Baring that, there is probably a short in the wiring somewhere. A short means the two wires used in trailer lighting are touching someplace.
Because lighting up the brake lights of both the car and the trailer pulls too much power. If the problem is a specific trailer then your trailer may be mis-wired. You may also have a mis-wired trailer wire adapter.