'02 Suburban - Dash Lights Dimming

[PAB_OH]

I have an '02 K2500 Suburban and a problem anytime I hook a trailer to it. Last winter I was hauling my tractor home from my mom's place, where I just cleaned her driveway, and I started to slide. The trailer was borrowed and did have trailer brakes but I didn't have a controller to operate the brakes. Anyway, I was on the brakes the whole way down a long hill and I noticed all the dash lights, including the radio, dimming everytime I hit the brakes. I thought it was something messed up with the trailer wiring.

Fast forward to today. I recenlty picked up a nice little 4x6 utility trailer and was hauling some stuff to my MIL's place and I noticed the same thing happening again. This time though I was going through an adapter since my 'burban has a 7 pin connector and the trailer has a 4 pin connector.

I noticed when I put the brakes on the lights on the dash would dim the same as before but when I would turn my turn signal on the lights on the dash would blink in unison with the turn signals.

I just repainted the trailer last week and checked all the wiring. At first no lights worked so I started checking the ground when I remembered the fuses. 3 of the fuses for the trailer lights were blown. I replaced them. After that everything was good but I noticed the front passenger side marker/turn signal bulb was blown. I replaced it and all the lights worked. I used my 4-way flasher to test the lights and the turn signal lever to double check each side individually. Everything checked out okay. It was dark out when I tested so I pushed the brake pedal and checked for the brake lights to light up to be sure they working too. They were. I don't recall looking at the dash while I was doing this since I was focused on the lights on the trailer so the dash lights may have been dimming when I did this but I didn't see it.

So has anyone encountered anything like this before? I checked the fuses when I got home this afternoon and they are all good. Lights on the trailer are all working as far as I can tell. I'm seriously confused.

I'm leaving for PA Monday morning on a bussiness trip but I'm taking my Suburban and the little trailer to pick up some turf tires for my Kubota I won on Ebay. I'm a little nervous about it. I know PA troopers are pretty tough on trailers. I don't want to risk loosing lights and not knowing it then end up with a ticket while travelling with my boss.

Any help is appreciated.

 

[SnowRidge]

It is pretty basic to check your trailer lights (and brakes, if electric) every time you hook up -- before you hit the road.

OK, I'll get off the soapbox. I would start by verifying that the trailer wiring is correct on both the tow and towed vehicles. Unless the connector on the Suburban is part of a factory wiring harness, it should remain suspect until you have verified that it is wired correctly. All trailer wiring should be suspect until verified, even that on a brand new trailer.

What you are describing could be caused by a miswire, short, or even an open ground, although it is less likely. You need to go over everything.

 

[Rara Avis]

Q: When I have my headlights on and apply the brakes all my lights on my trailer go out. What causes this?
A: You have a ground problem. In your situation, you have a ground that is strong enough to provide some lighting functions but not all. This is called a weak ground. When the taillights and brake lights are used at the same time it creates the maximum amp load of lights on the trailer. If a ground problem exists it will show at this point. The places to check grounds are as follows:

The connector on the vehicle should have a ground wire secured tightly on a clean surface to the frame. A wire attached to the body or a surface with undercoating, paint, or rust can cause a ground problem.
The connector on the trailer should have a wire from the connector secured tightly to a clean surface on the trailer.
Each tail lamp assembly at the back of the trailer also must be ground. This is done in one of two ways. The first is by a separate wire coming from the back of each tail lamp assembly and being secured to the frame. The second, and most popular, ground is achieved through the bolts of the tail lamp assembly. In this case, the lamp housing must be attached to the frame of the trailer. If the lights are mounted on wood or PVC material, the lights will not receive ground.
The last possibility to explore is in the trailer design. If the trailer has a tilting bed, it is possible the ground is not passing through the pivot point resulting in a poor ground. The solution to this is to route a ground wire from the connector at the front of the trailer to each lamp assembly at the back of the trailer bypassing this pivot point.
NOTE: The trailer hitch & ball connection area should never be considered sufficient ground.

Q: When I use one turn signal the other one blinks.
A: This is usually related to one of two things. The first could be a short somewhere in the system. All wiring and the vehicle connector should be checked and tested. The second andmost common cause is a weak ground in the system. Refer to the above question and follow steps 1 through 4.

 

[loulou61]

Go to Wally World or local auto parts place and they make a little tester for your trailer plug on your vehicle. It's a little 4 prong plug like on your trailer but instead of wires it has 3 little LED's to represent you R, L and parking lights plus brakes.
It's simple way to test your traier light system on your vehicle. I think it was only like $3.00.

Also check grounds. Faulty ground can act all kind of weird ways.


Lou
South Louisiana

 

[PAB_OH]

Thanks for the input guys. Sounds like it is likely the ground. I guess I'll just have to go through it from one end to the other.

 

[bdeboer]

I also have an '02 K2500 Suburban, and have had trouble with the 7 wire plug corroding. I have had to spray it with an electrical cleaner, and this helped. The first time it happened, I stopped at a Wally world about an hour from home and sprayed with battery terminal cleaner. I would also check or replace the ground on the trailer.

 

[workinallthetime]

1ST check the battery ground make sure its clean and tight
2nd the splice pack for your lights is
On the left upper I/P at the A pillar, there is a major splice pack there and that is where your lights are supose to be grounded. it looks like a real pain to get to and i cant imagine that being lose but thats th next step

 

[bdeboer]

"1ST check the battery ground make sure its clean and tight"


One other thing, I had trouble with a side post on the original battery not staying tight. When I got tired of tightening it, and replaced the battery before a long trip, I noticed that the threads inside of the terminal were stripped.

 

[PAB_OH]

Turned out to be a wire smashed on the passenger side. I noticed the lights on the dash coming and going in unison with the truck going over rough ground he other day. Narrowed it to the rear passenger light and started jiggling wires and was able to get the right turn signal to "lock up". Replaced all the lights and wirind last night ($19.99) and all is well today.

Thanks to everyoone who posted and gae me ideas on where to look.