I need to tap the great collective.  I have a shorelander double axle trailer for a boat i just got.  I have hazard, turn signal, and brake lights but not running lights when I turn the lights on in my truck.  The truck is a 2001 Yukon XL 2500 series.  I thought it may the adapter so I bought a new one but that was not it (adapter is round going to a 4 wire).  Is there a way to test the truck to confirm that it is sending the current when I turn my lights on?  Is there anything I should look for on the trailer other that the obvious frayed wire?  Thanks.  HORSE23

A volt meter?

I see a test light purchase in your near future.

It's tough to trouble shoot electrical problems without one (or a volt/multi-meter).


Look here for the correct wiring diagrams:

Trailer Wiring Diagram For 4 Way, 5 Way, 6 Way and 7 Way circuits

check the running light fuse in the truck.  my 06 1500hd blows it all the time

I have the same problem with one of my trailers.   Turns out I had a bad lead, I spliced into the license plate lamps to get running lights to fix it temporarily.

You do have working running lights on your truck, correct?

fuse
most newer GM's have a LOT of fuses
seperate ones for the trailer
if the truck works and the trailer doesn't, could very well be fuse.

also, hook the trailer to a different car and see if it's the truck or the trailer.

I just recently had a similar problem with my Shorelander trailer.  My problem was that I had a dim running light on the right side, and that blinker wouldn't blink.  Turns out that I had installed the bulb backwards.  The pins on the bulb are offset, and it is possible to put it in 180 degrees opposite of how it should go if you try hard enough.  It may also be possible that the previous owner has installed the incorrect type of bulbs in the trailer.

Do your lights look like the 5th ones down on this page?  http://www.sierraproductsinc.com/Site0708/TailLightsPage.htm