When I hook my travel trailer seven pin plug to my 2008 Nissan truck seven pin receptical, all lights work but the running lgts on my T.T; I think a fuse is blown, but I cannot find a blown fuse in the truck fuse box. Is there a in-line fuse in the tow package harness:

Do you have it hooked up to the ball when you are testing? 4 Leads covers L+R turn (2) Brake (1) and Running lights. You don't have a ground.

IF you have this trailer with this vehicle before the problem will probably in the wiring in the plug. Loose broken or corroded away. Check condition of the light sockets and earth points and wiring back to the plug

I would start by making sure the emergency break away switch has the plunger in it and it's working properly. If everything is OK with that then the 5 pin plug must be wired incorrectly. If you only tow the trailer with that truck I would suggest changing to a seven pin connector on the trailer. It would appear you also have a problem with the left trailer brake. They should work together.

Depending on what connector you are using, here is a link to the wiring diagrams:

http://www.etrailer.com/faq-wiring.aspx

You may have to use an OHM meter to test the leads at the tow vehicle side to verify correct placement. Good ground is essential too.

Check fuse 28 in the fuse block under the left side of the dash. There is also a relay for the trailer park lamps in that same fuse block. The fuse and relay are the trailer parking lamps and run independantly of the vehicles parking lights. You can also try backprobing the other trailer plug (you should have one 7 pin and one 4 pin) to see if there is power at the park light pin. If there is power at the other trailer plug than the fuse and relay are bad and you may have a bad/corroded plug or bad wring to the plug that doesn't work.

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If the other lights work on the trailer, it won;t be the earth return. Probably you have not wired the car connection to the same key as the trailer and your running lights are connected to pin 5 or the aux pin.

check for signal ground,this is not a metal ground, use a test light or volt meter to see if they at plug before you plug in the trailer, you may need to rewire the trailer.

First check the fuses. There may be one for trailer running lights. Check also power at the harness. If the brake lights and turn signals are seperate, there has to be a converter from 5 to 4 wire. For the power to feed back to the brake lights it sounds like the vehicle wiring is direct and not using a converter... or one of the bulbs on the trailer is contacting both contacts. Try http://www.etrailer.com/faq-wiring.aspx and maybe get a simple 4 pin tester that plugs into the 4 pin connecter. Hope this helps.

try this link www.dodgeram.org/tech/mods/electric/trailer_wire.htm see how i compare to what you have

You'll need to disconnect the wires from either the truck connector or the trailer connector...
I highly suggest purchasing a voltage checker- it looks like a screwdriver with a pigtail of wire with an alligator clip on the end. The tip of the 'screwdriver' has a point for probing. The light in the probe will light up...makes it easy to trouble shoot without a helper behind the trailer.
Hook the aligator clip to a good positive grounding point on the bumper or frame(not painted).
then pin by pin on the truck connection, stick the probe on each terminal tab.. and write a simple diagram where you find brake, tail, backup, etc...
Then i'd suggest, taking the connector off of your trailer, exposing the wire ends.
Run again thru your diagram and turn on each light of the truck. As you do, touch the wires from the trailer to that specific terminal. (make sure your ground wire is attached on the trailer) you can mark each wire with a piece of tape and label it which is which.
then simply attach your trailer wires according to your diagram to the terminals in the connector... that should get you in business..
hope that makes sense...
That way if the factory wiring harness remains the same, you'll be able to use it with other trailers if the need arises..