Hello,,

I am new to this forum and wanted to say Hi and check things out...

I am working on my 2002 Avalanche 4x4,,,  It has factory tow package and I am setting it up with a Draw-Tite Brake controller and the jumper harness to handle the 2 horse trailer I will be towing...  I received it used,, a few weeks ago,,, It did not have a hard life,,, However things will be getting tougher for it now...   It is factory wired for towing and has the 7 pin Pollack connector mounted by receiver...  I am using the 6 pin to 7 pin adapter...

When we first plugged in the trailer ( Before the brake controller and jumper harness were installed ) a few weeks ago the Flashers and Running Lights on trailer lite up fine..  However after a short tow the right directional was the only light that worked...  At this point the horse trailer was parked and everything on the truck seemed to be working properly... We also use the truck to tow other trailer and noticed that those lights were not working properly either and they were working fine last time the trailer was used... 

After checking all three trailers,, each having a different wire adaptor and using a different tow vehicle I found that the trailers were operating properly with the exception of a blown bulb here and there...

I started checking the truck and found 3 blown fuses in fuse box under hood,, all in the trailer wiring location of box and one other blown fuse in the exterior light spot...  After replacing all the fuses I then found both bulbs at the rear plate blown and when they were replaced only the right one would light... 

I have since started tracing wires under rear of truck and found a junction block at the right side under the inner quarter panel behind rear wheel... It is tucked up and mounter to inner panel with 4 harnesses going into it...  The largest of the harnesses seems to lead to the trailer connector,,, The other 2 seem to go up into the bed on either side and the smallest and last one has 4 wires and they all go directly to the rear plate lights...  By probing the small harness connector and checking the output of the junction block I found the terminal feeding power to the left plate light is dead...  For testing purposes I removed that wire from connector at the box installed a in-line 10 amp fuse and jumped it to the power lead to the other working light...  Now both light are working fine and no fuses have blown yet...  While I was performing these tests and inspections I also found that someone had already performed some similar wire alterations to the harness at the junction block...  I have not chased that alteration yet but it looks to be one wire cut from the large trailer harness connector and jumping to one of the other two harnesses that go into this connector....

My questions about this would be,,,  What in fact is that junction box for,, is it something that must be replaced and the the wire returned to there original positions in the harness???  OR IF the repairs performed seem to leave all systems operating properly can these repairs stay so I don't need to purchase a part ???  And what is this junction box for,, is it just a place for these harnesses connect instead of being completely hard wire into main harness of the truck ??? 

I am sorry for being so long winded about trying to explain these conditions to you...  This truck and horse trailer have a long trip coming up and the only thing not working yet is the left turn and brake light on trailer...  I have switched out bulbs but the wire is dead at the lamp and harnesses is enclosed in the box channel of the trailer frame making it very hard to access for further testing...