Please Help I’m Fed Up...

[AlwaysFishing23]

I know this forum gets very little people now days but maybe someone could help me out. So I purchased my self a new ( to me) 2000 Silverado 1500 back in August. Be mindful this is my first truck/vehicle. So I tow often ( boat, snowmobiles, atvs, kayak). But the guy I bought it from had said all trailer lighting works great. So I didn’t think much of it. Well a few weeks after I bought it I hooked up a trailer to try the lights.... well. All running lights work perfect, but, no drivers side signal or brake light, passenger side brake light and signal work great. I have tried 3 different trailers and have tried them on 2 other vehicles everything works great. So first thought is Check fuses right? So it was in at a Chevy dealer getting some work done so I had them cheak it out. Fuses all look good and they told me all trailer lights work perfect. So I thought well maybe my 7 pin to 4 flat adapter was bad. I bought a new one of those and tried again. I got one with the test lights on it and sure enough all lights worked great UNTIL I hooked up a trailer. When I did this it kicked out the drivers side brake light and signal on the trailer. At this point I’m feed up with this issue and I’m to worried about getting nailed so I only tow a little ways from home. Anyone have any thoughts on what this could be? I was thinking maybe a bad ground on truck? But how would you know? And also this truck has spent it entire life in Florida until last May so this is the first winter in MN. But it shouldn’t matter since I tried the lights back in the end of August. Thanks a lot!

Edited February 22, 2019 by AlwaysFishing23

[leech~~]

Sounds like it may be a bad harness on the trailer it's self.  Get one of these and test the truck again. If all works it's time to fix or replace the trailer harness. I've done both on the 5 different snowmobile trailers I have had over the years. It could just be a bad corroded or shorted rear light fixture on that one side or a shorted wire on that side.

 

ATB 16687 Truck Trailer Vehicle Plug Tester 7 Round Blade 4 Pin Wire Light Brake RV Tow

 

Edited February 22, 2019 by leech~~

[AlwaysFishing23]

Thanks for the response leech. I purchased an adapter similar to that one with the test lights. Both trailers I tried are almost new and both have LEDS. All work great with Moms SUV and Dads truck. I’m thinking it has to be somthing corroded or a broken wire on the truck end. But figuring that out is out of my reach.

[leech~~]

Not the best time of year to be laying in the cold and slop under a truck tracking down wires but I have done that as well.

Sounds like you then need to track down the yellow wire on the truck and see where it may be corroded and shorted somewhere.

 

[PurpleFloyd]

They are probably wired differently. I’ve seen this happen. 

 

Actually I had a brand new 2015 Silverado 2500 diesel issued to me as a company vehicle and had issues galore with the factory wiring and the gooseneck trailer I was pulling. It was the biggest nightmare I’ve ever had and it was all with the factory Chevy wiring and integrated brake controller. 

 

[Hoey]

Trailer, one side, brake and turns dont work, same wire, same bulb filament.  Sounds like a ground problem.  With other tow vehicles its ok.  Are these 7 pin to 4s?  Could be the wrong adapter?  Not all 7 to 4 pins are the same.  Sometimes too that bad ground seeks its path through the hitch.  

[Hoey]

Make sure the adapter wiring matches the diagram on the cover of your female plug-in on your truck too.  Some use the center pin for backup lights,  yet others it is an auxiliary.  Also make sure that the lobe on the male is lining up with the lobe on the female plug-in too.

[fishingstar]

I had problems with my 02. I found that the plug on the truck side going to the plug at the bumper was corroded. I hope that made sense I cleaned it up and put dielectric grease on it. 

  

[Wanderer]

10 hours ago, fishingstar said:

I had problems with my 02. I found that the plug on the truck side going to the plug at the bumper was corroded. I hope that made sense I cleaned it up and put dielectric grease on it. 

  

 

I had to do the same fix on my ‘Ol 96er.

[Jeremy airjer W]

20 hours ago, Hoey said:

Trailer, one side, brake and turns dont work, same wire, same bulb filament.  Sounds like a ground problem.  With other tow vehicles its ok.  Are these 7 pin to 4s?  Could be the wrong adapter?  Not all 7 to 4 pins are the same.  Sometimes too that bad ground seeks its path through the hitch.  

 

Bad grounds  make trailer lights do odd things. Tail llights work until you step on the brake then nothing works until you let off the brake. Tail lights off and all the lights flash when using the turn signal. It is likely not a ground issue.

[Jeremy airjer W]

Here is what I would do. Hook up the trailer and turn on the 4 way flashers or hold the brake pedal down. Now you have a known good on the right side to compare to. Go to the fuse box under the hood and locate the "TRL L TRN" and "TRL R TRN" fuses (both 10 amp fuses). With either a test light or a multi meter check the fuses for power. should see 12 volts on both or the test light should illuminate brightly. If the right side does and the left side does not, unplug the trailer and recheck. If the left side fuse now shows power the problem is in between the fuse block and the turn hazard switch or the turn hazard switch itself.

 

If there is good power at both of the fuses than the problem is in between the fuse block and the trailer plug. Power is going away as soon as you plug in the trailer which tells us there is probably a corroded wire in that circuit. If you where to measure the voltage at the trailer you will probably find there is still a small amount still present on the circuit. Corrosion = resistance = voltage drop under load.

 

You will be looking for the yellow wire that runs from the fuse block to the trailer plug. There are typically connectors in the harness near the rear of the vehicle. Find that wire in the connector and back probe it with trailer connected. If there is 12 volts the problem is towards the trailer. If there is not 12 volts the problem is towards the fuse block.

[bowhunternw]

I had a 04 Silverado that was a pain for trailer lights. Never really go it fixed, but I believe that there was a bad ground to the harness or just a bad  connection. I could grab all the wires on the truck side of the harness and wiggle them around and the lights would work right for a while, only eventually the problem would return.

[AlwaysFishing23]

Really appreciate all the feedback guys. I took a look under the truck on Saturday but with all the salt, ice and snow packed underneath it was impossible to see anything. But at least I have all your replies so this spring or summer I can look back and be able to start tracing this issue, not sure if I’ll get a different truck next fall or not but either way I’d like to resolve the issue.