No power at the back of the truck for trailer

look at other lamp fuses, sometimes an seemingly unrelated fuse will be the power source for your non powered fuses.

It is uncommon to have all trailer lights non operational at the plug. Make sure you are using a known good test light and have a GOOD ground supply when testing for power at each individual pin. Depending on make and model, some do utilize fuses that should be checked as well

It's a very good possibility that it is the trailer. You say that it is new, is it a brand new trailer or just new to you? If it is brand new, and you bought it from a place that deals with trailers, then I would say take it back and have them look over everything. If that's not an option, then it's time to pull out the circuit tester and start checking wires. See if you are getting power to the Blue wire on the trailer, and if so is there power all the way to the brakes. You will need someone to push on the brake pedal while checking the wires. If the power is good all the way to the brakes, then you will need to pull the drums and inspect the brake shoes for wear, and condition of the the brake components. If this is a used trailer, then it would be a good idea to do this anyway so that you can also inspect and grease the bearings. If everything looks good, then the brakes might just need to be adjusted via the slot on the back side of the brake housing. If no power is seen in the blue wire, check the Red wire (12v Aux/charging), if it doesn't have power, then you more than likely have a Ground issue. This can easily be checked by hooking the trailer to the truck (hitch). Both use a chassis ground, and will use the hitch itself as the ground connection, though it is not a good idea to use it as the ground point.

This is most likely an issue with the wiring harness going to the connector on your truck you need to start at the connector at the back of the truck and walk your way forward to the breakers under the hood (rarely is the 12 power on the trailer harness connecter simply fused since it is a higher current circuit, it usually uses a breaker just like your headlights). Before you do this find a copy of the wiring diagram for your truck so you know what you are looking for. Also a dead battery normally will not fully charge in the normal time span of a trailer being towed as you can typically figure over 6 hours to charge the type of battery (deep cycle) that is in a trailer.

get the standard wiring design
http://www.narva.com.au/products/browse/wiring-diagrams
Yellow is the left turn signal on pin 2
Check trailer plug and see if correct colors used on trailer plug
Would suggest getting a 12volt probe so you can test the car socket when left indicator is going on - flashing
To check that the correct pin has 12volts flashing left on it.

Did you make sure you have a good ground? I had to install an additional ground wire from my trailer frame to my truck frame to make sure that I have constant ground so that things don't stop working.

But you should also check and make sure that you have the right wiring to operate back up lights in a trailer. Normally the flat four wire type connectors are not designed for a trailer with back up lights.

then if theres power to harness at back of truck its the harness on trailer or wireing on trailer

7 way trailer lights:
Black- 12 volt (power)
Brown- tail lights
Yellow- Left turn signal
Green- Right turn signal
Blue- Brakes
White- Ground
Orange- Auxiliary power (not always used, but example would be trailer back up lights, if equipped

This is a trailer question, but I will try.. Connection is broken between pin and connector so no power will pass....Buy a new plug. Sorry.

Check your ground wire. If it's ok, take a test lead and check for power in the plug on your truck. If still no power trace the wires at the back of the truck to where the plug for your trailer light hooks into the truck lights make sure the conection is good and the plugs aren't corroided.