Trailer Wiring Problem

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jaxbuckeye

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Nov 30, 2012
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My new (to me) Viking PUP trailer has a 7-pin "round" electrical connection including electric brakes.  My vehichle just has the standard 4-pin flat rectangle receiver on its hitch.  I bought an adapter for it but the trailer lights still won't work.  I've double checked both the adapter plugged into my vehicle and the trailer lights both work, but still nothing.  Has anyone had a similar issue?
 
jaxbuckeye said:
My new (to me) Viking PUP trailer has a 7-pin "round" electrical connection including electric brakes.  My vehichle just has the standard 4-pin flat rectangle receiver on its hitch.  I bought an adapter for it but the trailer lights still won't workI've double checked both the adapter plugged into my vehicle and the trailer lights both work, but still nothing.  Has anyone had a similar issue?

I'm a little confused, the adapter and trailer lights work, but the trailer lights don't work?? Also, how do you adapt a four way to a seven way without adding additional wires. Are there separate wires for battery charging, electric brakes, and backups? If you are all hooked up according to specs, and nothing is working, I would take a look at ground connections first.
 
Here's the adapter I have:  http://www.etrailer.com/Wiring/Tow-Ready/30717.html  When the 4-pin side of the adapter is plugged to my 4-pin harness on my vehicle, the 7-pin side of the adapter works.  The trailer lights work as well, however when I plug the 7-pin trailer harness into the 7-pin adapter the trailer lights don't work.  I hold the ground wire to my hitch. 
 
jaxbuckeye said:
The trailer lights work as well, however when I plug the 7-pin trailer harness into the 7-pin adapter the trailer lights don't work.  I hold the ground wire to my hitch. 

I guess I'm just dense...still don't know how you're getting your trailer lights to work without plugging in your harness unless you are using jumper wires. If you are using jumper wires to light up your trailer lights while holding a ground wire to your trailer frame, but don't have the ground wire on the frame when plugging in the harness, I would check the ground connection in the harness plug.
 
I'm having the same confusion as Dennis is. There's something inconsistent in your description, as you have me wondering whether the trailer lights are workiing when they are disconnected or whether they are not working when connected or...  :-\
 
With that adapter in place you need to probe the wires and see if the power is coming through. Like my common test is to turn on the hazards and probe the wire looking for a pulsing light. That way you don't confuse solid on brake light or running light for a power source. Yellow and green should be the pulsing light and you should be able to follow that all the way back to the trailer taillights. Then turn on your running light and follow the brown wire all the way back. Now I should talk about ground first but better late than never. The white wire is ground make sure is good between the TV and Trailer.
 
Take the adapter and throw it in the garbage can or return it if you have the package still.  Then go online and search for the Bargman wiring diagram and cut off the 4 wire plug you have and rewire it for the correct 7 wire configuration.
 
donn said:
Take the adapter and throw it in the garbage can or return it if you have the package still.  Then go online and search for the Bargman wiring diagram and cut off the 4 wire plug you have and rewire it for the correct 7 wire configuration.

Rather blunt... But he's right...
 
Add me to those who are confused.  The flat 4 pin connector on your tow vehicle won't power the trailer brakes anyway, so you will need to modify the tow vehicle to add a trailer brake controller and a 7 pin connector that matches the trailer.

I've never even seen an adapter designed to couple a 7 pin on the trailer to a 4 pin on the tow vehicle, since the 4 pin cannot supply all the necessary signals for the 7-pin on the trailer.  There is, however, a device that plugs to a 4-pin on the vehicle side and had extra leads allowing you to easily add the brake and other circuits needed for the 7-pin. Is that what you are using?
 
Sorry - After reading my description again, it is confusing on the part about the trailer lights.  I know they work, because the guy I bought the PUP from had a 7-pin plug on his truck and he showed me the trailer lights work.  However when I use the adapter to plug the 7-pin trailer into my 4-pin hitch on my tow vehicle, the trailer lights don't work. 
 
Lets start simple here....

Get a test light.
Check the 4 way plug on your tow vehicle. 
If all is working there, Then connect adapter and test each terminal in it. 
If that works then check for a positive ground.

You may have a plug on the Trailer or tow vehicle that is not wired properly and is sending power to the wrong prong on the plug.

BUT,  If I had guess....  Most likely a ground issue.
 

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