How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Mike S. Your Own Question
Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 6793
Experience:  ASE Certified Master Technician
20625509
Type Your Chevy Question Here...
Mike S. is online now
A new question is answered every 9 seconds

Suspect poor ground for trailer wiring. Unless trailer runs

Customer Question

Suspect poor ground for trailer wiring. Unless trailer runs LED lights I seem to have a back feed through both signals
JA: Just to clarify, what are the exact lights you're talking about?
Customer: If I hook up to a trailer without led lights in it and turn on one signal either left or right I can watch both blink on the trailer and also makes my signals and brake lights flash on the truck
JA: What is the model/year of your Chevy?
Customer: 2004 2500hd with the lb7
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes. Ive pulled apart the trailer plug and double checked that I don't have any wires touching inside. Ive spliced into the ground wire before the trailer plug and attached it to the frame and about to clean as many grounds to the frame that I can find. ex: below the drivers door to frame, between cab and box on lh side on frame and under battery at the front lh side to the fframe
JA: Anything else you think the mechanic should know?
Customer: The truck played tricks on me a few years ago and I found it to be the big relay under the dash so I replaced. Checked it as well just lately and its ok. Noticed this issue seemed specific to one trailer and I found it to be the trailer giving me issues but now this exact problem has been traveling with the truck to multiple trailers that used to work fine in the past
Submitted: 3 months ago.
Category: Chevy
Customer: replied 3 months ago.
Also without truck hooked to a trailer and just using a test light at the trailer plug with either signal on I have power to both left and right pins at the connector
Expert:  Mike S. replied 3 months ago.

What are the type bulbs you are using for the trailer turn signals? The normal type bulbs that is.

Customer: replied 3 months ago.
Im not worried about the trailer because without truck hooked to a trailer and just using a test light at the trailer plug with either signal on I have power to both left and right pins at the connector
Customer: replied 3 months ago.
I suspect its just a poor ground because of the back feed of power. Is there a specific ground location or spot along the frame that you have seen give grounding issues?
Customer: replied 3 months ago.
Expert:  Mike S. replied 3 months ago.

Sorry, I was out. Why didn't you answer my question?

Customer: replied 3 months ago.
I did. The trailer is not part of the system at the moment and still have issues but if you need to know one trailer runs an 1157 bulb and the others have a sealed housing with an internal bulb and others run an led sealed housing light.....
Expert:  Mike S. replied 3 months ago.

What do you mean the trailer isn't part of the problem right now? So, you have the trailer unhooked and you still have problems with the lights on the truck?

Customer: replied 3 months ago.
Yup. With a test light I can see power on the yellow wire and the green wire of the trailer connector when i have my left hand signal on.When I turn my right hand signal on I have power at the yellow wire and the green wire at my trailer plug connector.Sounds like the yellow and green wires are touching BUT when a trailer with led lights is plugged into the trailer connector of the truck the system works as it should.When a trailer with incandescent bulbs is plugged into the trailer connector of the truck and i turn the left hand signal on both left and right hand of the trailer blink and is backfeeding into my truck making the left and right hand signals blink as well as the brake lights on the truck.
Expert:  Mike S. replied 3 months ago.

Ok, yes than you have a short, the green wire should be for right trailer turn. The yellow is for left trailer turn. So, the problem is with the truck, you are correct.

So you have both trailer turn signal wires hot no matter which way you turn the truck turn signal switch to, either left or right.

Wait, why are you saying when you hook up trailers with incandescent bulbs the bulbs act up when they already act up with a trailer hooked up.

Any who how, I think you should double-check all of the bulbs on both the truck ad trailer and make sure they are the correct bulbs. At least the truck I the trailer is not yours.

Expert:  Mike S. replied 3 months ago.

The ground by the way for that trailer connector should be G302 located at the left side of the fuel tank.

Expert:  Mike S. replied 3 months ago.

Here is the wiring diagram, for what it's worth cause this is going to be a tuff one, but I'll help you through it.

Expert:  Mike S. replied 3 months ago.

Now I am no bulb expert but I believe the 1156 are single filament and the 1157 are two filament, plus I believe there is the 2057 and I believe they are an updated version of the 1157 but don't quote me on that one.

Expert:  Mike S. replied 3 months ago.

Check the voltages at them 2 fuses, the rt trlr st/turn and lt trlr st/turn , if you get the same results there, I believe you are looking at a faulty turn signal flasher module.

Customer: replied 3 months ago.
Cleaned trailer wiring ground and attached back to frame.Still having issue.Checked voltage at fuses. Yes when signal is activated with trailer connected i have voltage at both fuses BUT without trailer connected it is normal. Isnt that expected if i have power back feeding?
Expert:  Mike S. replied 3 months ago.

Yes, a power source will find ground through any source that it an and it will always take the path of least resistance. So, let's say for instance a wire was short circuited to another wire, the ground path could change from the first wire and take the second wires path, even if it happens to be a normally positive wire, it doesn't matter as long as it has a path to ground that is less resistance then the first.

That is why I wanted you to check all of the bulbs, cause with the wrong bulb in a socket say a single filament instead or a double filament, the power could possibly be touching the ground spot at the bulb as well as the power spot both at the same time and sending power back through the power circuit of let's say the parking lights and then head over to the other side and finding a ground through the turn signal on that side and back along the power wire back into the truck and so froth.

Customer: replied 3 months ago.
But without a trailer connected i can make a test light blink on both turn signal pins at the trailer plug.My thought was the incandescent bulbs draw more power than an led does and gives me this issue causing weird things to happen to both truck and trailer. Hence looking for problematic grounds.An led is also just a diode so power cant travel backwards through it
Expert:  Mike S. replied 3 months ago.

That is why I said to check all of the bulbs, that includes on the truck as well

Expert:  Mike S. replied 3 months ago.

Let me ask, are you using a metal ground when testing at the trailer plug or are you using one of the terminals in the plug as a ground for the test light?

Expert:  Mike S. replied 3 months ago.

Yes, an LED is a light emitting diode and voltage only flows in one direction.

Customer: replied 3 months ago.
Test light grounded to hitch.Truck has led lights
Customer: replied 3 months ago.
If the large relay behind the kick panel was giving issues i would have seen voltages on both fuses without the trailer connected correct?
Expert:  Mike S. replied 3 months ago.

Which relay, the "park lamp" relay? No, that is not part of the trailer turn signal circuit at all.

Customer: replied 3 months ago.
No the large one for the trailer circuit. Its behind the kick panel to the left hand side. Directly behind the interior fuse panel
Expert:  Mike S. replied 3 months ago.

Do you know the name of it?

Expert:  Mike S. replied 3 months ago.

Are you sure it's a relay and not that module?

Customer: replied 3 months ago.
In the wiring diagram 3 of 3 its labeled as i/p relay block (near left kick panel)
Customer: replied 3 months ago.
Yea you can call it a module i guess. looks like a big relay. take it apart and it looks like 2 relays in 1
Expert:  Mike S. replied 3 months ago.

Well, that is the ground for the module. If the voltages are correct at them fuses I mentioned, then I don't think it has anything to do with that relay, module and/or ground G203.

Customer: replied 3 months ago.
14ga wire for a ground wire going into the trailer connector to small? I don't know what i did but with a test light and no trailer connected system works good now. as soon as i plug a trailer in with incandescent bulbs i have problems. added another wire to the ground circuit from trailers plug to the trucks frame and then system works fine
Expert:  Mike S. replied 3 months ago.

So you are done, the ground was bad?

Customer: replied 3 months ago.
Im asking if a 14ga wire is to small for the circuit on these trucks? And then i told you what happened what i did to come to that question....
Expert:  Mike S. replied 3 months ago.

You can test the ground voltage drop in order to tell if it's loosing any voltage.

Hook up a dc voltmeter the positive lead as close to the ground wire on the trailer connector as you can, then hook the negative test lead to a good metal ground or on the battery negative post, to be sure. I have a 25 Foot wire I use just for that. Anyhow, when the voltmeter is hooked up, power the circuits and watch the voltmeter. It should read no more, than 0.2 volts. If it does that is the amount of voltage drop and how much that ground wire is loosing cause the ground will take the path through the meter instead or the wire if the meters résistance is lower and the wire will also measure how much voltage is flowing through the meter when it should be flowing through the ground wire. So, if the voltmeter reads anything over 0.2 volts, that 14 gauge ground wire isn't enough.

Expert:  Mike S. replied 3 months ago.

What was the voltage drop/loss along that 14g ground wire?

Expert:  Mike S. replied 3 months ago.

Did that answer your question? If so, kindly leave me a positive rating, so I get credit.

Related Chevy Questions