Trailer Light Troubles...HELP!!!

[Doctrt]

Hey Guys,

Hopefully someone can help me with this because I'm about to pull my hair out. Let me start out by saying I think the problem is in my vehicle (an '03 Trailblazer) and not the trailer itself. I've grounded all the lights properly directly to the frame (ground away the paint) as I know this is usually the problem. I went to Princess Auto and picked up a trailer light (four way plug) tester. After bipassing the entire 7way hookup (RV) and going straight to the wires upstream of the harness I solved some of my problems but here's what I'm left with. Right signal - fine. Left signal - fine. Running lights - fine. Brakes - only left side goes bright. Further to that, when I press the brakes with the right turn signal on the left turn signal blinks. Now to me this sounds like a grounding issue as it doesn't make a lot of sense but the ground wire is clean and even when I connect it directly to the frame of the truck, I get the same result. One more trip to princess auto, and I get a 5 to 4 way converter hopefully will solve my problem but I'm not sure what to connect the fifth (red) wire to. I do have a thick red wire on the truck left although I think this is auxillary power. I also have a thin green wire - back up lamps and a thick blue - trailer brakes. At this point I'm very confused. Please help!!

[jjcanoe]

the prob is not the vehicle it is in the wire harness to the right tail light. There should be 3 wires to the harness. Black should be the ground. Leave the Black alone and switch the other 2 around and that should solve your problem.

 

 

jjcanoe

 

Scratch all that! I re-read the post and now I'm confused as well.

 

Your best bet would be to get a trailer wiring kit from P. Auto and start from square 1. That's the first thing I did when I bought my boat. Never had a problem since and even found some corroded and bare wires on the old set which may have caused problems down the road.

 

jjcanoe

Edited April 14, 2010 by jjcanoe

[Fisherman]

Do you have a 4 way plug at the rear of the Trailblazer,(1 ground and 3 hot)? Check that with the tester, pin 1 is signal/brake right, pin 2 is signal brake left, pin 3 is park/running lamps. If you have a left signal flashes with the brakes and right signal on, then you are most likely right, bad ground. Pull the bulbs out, clean the inside of the sockets with an eraser tip, clean the bulb bases and contacts and then grease with vaseline. I'll bet that 99% of trailer light faults are ground issues. Personally, I run a dedicated ground wire to each of the lamp bases, soldered and liquid taped, no more problems.

[DanD]

I’m thinking that where your problem is, is the truck’s rear lights, use six different circuits to run the rear lights; left turn, right turn, stop left, stop right, back-up and parking lights

From what I got from your description, is that you’re trying to get the four circuits of the truck's turn & brake light circuits to work on a two circuit trailer setup; left turn/stop, right turn/stop; the parking lights are on their own circuit for both sides.

The manufacturer has combined the stop and turn circuits for you, when they ran the factory trailer plug, via the combination turn signal/four way flasher module.

You’re right about the red and blue wires they are auxiliary (red) power and trailer brake (blue).

At the trailer plug harness; the yellow is left turn & stop, the dark green is right turn & stop; brown being parking lights for both sides. The light green is for back-up lights; which I’ve yet to see on a small trailer; so why? LOL

The white wire as in all trailer lighting circuits is the ground.

So if by chance you’ve been trying to tag into the dark blue and light blue wires (stop & turn) for the actual lights of the truck; you’ll need to make another trip to P.A. and buy a splitter box that will combined the four stop & turn circuits into two circuits; via its electronics.

Like I said the manufacturer has already done this combining for you so I would try using that 7 wire harness to connect the trailer light; using only the circuits you need.

There are fuses hid all over the place for the lighting systems on these trucks; under hood, dash and back seat, so make sure they are all still ok

I have the wiring diagrams for this truck’s exterior lighting circuits; they may help you understand my ramblings. If you want them PM me your email address and I’ll send them to you.

Dan.

[skeeter]

keep in mind that a lot of trailer lights have there own ground aswell.

right at the light.

i had the same problem on my snowmobile trailer,

once i fixed the ground wire at the light/frame it worked proper.

 

the 5-4 converter is for vehicles with yellow turn signals.

 

[Doctrt]

Do you have a 4 way plug at the rear of the Trailblazer,(1 ground and 3 hot)? Check that with the tester, pin 1 is signal/brake right, pin 2 is signal brake left, pin 3 is park/running lamps.

 

This is what I have. I've actually isolated this from the 7 wires upstream of the RV plug. Like I said, the three wires (blue, red and light green) are not used. When I plug the other 4 into the LED tester I get a good left turn, a good right turn and good running lights (back and orange/side). The problem is when I hit the brakes, I get only left brake light - on the tester as well as the trailer, so the problem has to be in the vehicle.

 

Is it possible that the front end of the ground could be as corroded as the back end was, or did I eliminate this as a possibility by grounding directly to the vehicle and getting the same result? I like the idea of the fuses. I've only checked fuses under the hood. I'll have to look and see if there are any more under the seats or dash. Still confused, but I appreciate all the suggestions.

 

Thanks again,

 

Tim

[Fisherman]

This is what I have. I've actually isolated this from the 7 wires upstream of the RV plug. Like I said, the three wires (blue, red and light green) are not used. When I plug the other 4 into the LED tester I get a good left turn, a good right turn and good running lights (back and orange/side). The problem is when I hit the brakes, I get only left brake light - on the tester as well as the trailer, so the problem has to be in the vehicle.

 

Is it possible that the front end of the ground could be as corroded as the back end was, or did I eliminate this as a possibility by grounding directly to the vehicle and getting the same result? I like the idea of the fuses. I've only checked fuses under the hood. I'll have to look and see if there are any more under the seats or dash. Still confused, but I appreciate all the suggestions.

 

Thanks again,

 

Tim

It's a good possibility at it seems your one brake light may be acting as a ground return on the trailer(sounds wierd, but it happens).

If you are not getting power on the plug end your truck for brakes, then the problem is in the vehicle. Some vehicles do use a separate fused section for trailer plugs.

[Tybo]

Sounds like you have a wire that's breaking down.

there is only a couple of strands left and you can't pushenough amperage through.

If you have a multimeter, Plug it into the trailer socket on the SUV for the light not working.

Hit the break. If there is a voltage drop.

You have a bad wire.

[johnyd]

I think you said that you have a 7 pin RV plug on the truck already and are hooking into the wires above it. Just go to the P. Auto and Buy a 7-4 pin reducer that is what my dad runs on his yukon for his trailer.That works fine and your not splicing tapping and hacking up your wires.

 

Good luck i absolutly hate wiring issues.

[smally21]

like the last poster stated did you have working lights at the bargman? the 7-4 adapter is probably cheaper than the 4 way tester. why are you going above the existing connector instead of using it? vehicles without factory harnesses require a module to isolate/provide the required signals for your trailer wiring system - that is turning a signal for one light into a signal for two. in a vehicle with a factory harness (just about anything these days) the work is done for you all the way to the bargman (7pin) connector. forget all this talk of grounding and frayed wires and plug an adapter into your truck and test that. if your existing 7pin fails to provide the required signals to the 4 way adapter then lets talk wiring....

 

hope i understood your issue correctly

[Doctrt]

Update-

 

Well, I think I've taken this boat as far as she's gonna sail. I've hardwired everything together, soldering and heat shrinking all connections (green, yellow, brown and white) on the truck side. What I'm left with is working signals, running lights and still only the left brake light coming on. I've actually solved the problem with the brake + right turn resulting in the left turn signal coming on by doing this. In fact I did notice both brake lights coming on properly but only for a minute. It's clear now that the ground on the truck is faulty somewhere along the line, but grounding directly to the truck frame didn't solve the problem. I think this is as far as I'm gonna go, but I still welcome any suggestions. Thanks again for all the help.

T

[vinnimon]

Update-

 

Well, I think I've taken this boat as far as she's gonna sail. I've hardwired everything together, soldering and heat shrinking all connections (green, yellow, brown and white) on the truck side. What I'm left with is working signals, running lights and still only the left brake light coming on. I've actually solved the problem with the brake + right turn resulting in the left turn signal coming on by doing this. In fact I did notice both brake lights coming on properly but only for a minute. It's clear now that the ground on the truck is faulty somewhere along the line, but grounding directly to the truck frame didn't solve the problem. I think this is as far as I'm gonna go, but I still welcome any suggestions. Thanks again for all the help.

T

A quick qustion for ya.When you have a left or right sinal on, does the signal display on your dash blink quickly?And in doing so hit the brake pedal, does it slow down and become brighter on the dash?Have you replaced your signal flasher after rewiring and trailer hook up?Do you have LED lights on your trailer?Do yourself a favour,run a ground wire from your battery directly to the tailer end of the harness and check.Then report.

[DanD]

I hope I understood your last post correctly; as in all lights are working, other then your right side brake light?

If so and you can run a combination of lights as in right turn flashing and parking light; with them working normally; then its not likely a ground issue.

I would go and find the turn signal/hazard flasher module under the left side of the dash.

This module is not only the flasher unit for the vehicle; it is also the (lack of better word) splitter for the brake and turn signals.

With you saying that the right signal is working; that tells us that the dark green wire from the flasher module to the trailer is good. This same green wire is the brake light wire for the trailer. We also know that the module is receiving a brake light signal from the brake light switch because the left brake light is working.

What we need to know is whether the flasher module is sending out a brake light on the Dr green wire at the module. The module may have lost the ability to make this internal electronic connection but sill allowing all other functions.

Again this module is under the left (drivers) side of the dash. It’ll have a 10 wire connector on it, labeled alphabetically from A to K; these letters are printed very small and are hard to see. Well at least for me; I can’t see them without my glasses. LOL.

The terminal in the connector, you need to check is “D”; which is one of the two dark green wires at the module. The other dark green terminal “F” is the left turn signal input from the turn signal switch. The letter designations should be on the connector’s side.

Here is the connector’s terminal lettering and what they are; they skip the letter I.

A- Lt green wire: Right turn signal input from switch

B- White wire: Brake light input from brake light switch

C- Yellow wire: Trailer left turn/brake output

D- Dr green wire: Trailer right turn/brake output

E- Black wire: Module ground

F- Dr green wire: Left turn signal input from switch

G- White wire: Hazard input from switch

H- Yellow wire: Left turn output to fuse panel under rear seat

J- Tan wire: Right turn output to fuse panel under rear seat

K- Orange wire: Battery power feed (hot at all times)

Not all of these terminals are power some are grounds; all we’re concerned with is if there is power on the Dr green terminal "D" wire, when it should have (brake applied or right turn).

Now with a test light clipped to a known good ground and the probe connected to the Dr green wire “D”; the test light should light steady, with the brake peddle applied and then flash with the right turn, turned on. The module must remain connected during the test. Why I suggest using a test light is that it applies a load on the circuit; where a voltmeter will not. Sometimes a circuit will need a load applied brfore it will show a fault.

 

Keep it fun and let us know what you find.

 

Dan.

Edited April 15, 2010 by DanD