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Discussion Starter #1
I'll try to be specific here.. I have a 05 Envoy SLE. I have not running lights on my trailers. I hook the trailer to my other vehicle everything lights up. I have a 7 rnd to 4 flat adapter. All my fuses seems fine. I have 4-5 I think. Trailer, trlr lft brake, trlr rght brake, trlr BU. maybe another, I forget. I think its the Trailer one that I need to be worried about. Its a 30 amp fuse. its not blown.
Is there something simple I can do to test. I assume its one wire from the fuse box all the way back to the plug? I'll check both ends to see if its loose. Anything else?

Thanks
Jason
 

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2005 gmc envoy_denali
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I'm sure you have already checked this, but is the red wire under the hood by the fuse box properly attached? They come unattached from the dealer or factory.
 

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2002 chevy trailblazer_lt
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Run a test ground wire from your trailer frame to a ground on the truck. I had the same problem and it fixed mine. Some trailer connections work fine as the hitch ball will be a good ground for the lights. My TB was not good enough. I had turn signals, brake lights messed up but as soon as I made a good ground from trailer to truck they worked fine. I initially thought the 7-4 adapter was bad but used the test light at each location in the adapter and it worked as advertised. Checked the trailer lights on another vehicle and they were fine. That left only one thing, a bad ground on the trailer.
 

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Discussion Starter #4
Envoy Fan: Isn't the RED wire for the 12v AUX. power?? I actually didn't check that.
I will check it tonight.

bullethole: I am 99% positive it has nothing to do with the ground. I actually never connected the ball and hitch. this has happen on two different trailers now. I have a pop-up that didn't have running lights. I assumed it was the pop-up. (just bought it used). now I hooked up my utility trailer and no running light either. I have no power at the Envoy 7-pin plug for running lights. It has to be the plug !! Right ??

What kind of voltage should I be getting at the plug. if I am touching the ground and stop lights with a volt meter. and I hit the brakes, what should the volt meter read or do ??

Thanks
jason
 

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2004 gmc
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jgray_22 said:
Envoy Fan: Isn't the RED wire for the 12v AUX. power?? I actually didn't check that.
I will check it tonight.
You're right. And AUX power is never one that is passed through the 7->4 adapters, since most trailers don't need it. Neither does the brake wire go through the 7->4 adapters.

bullethole: I am 99% positive it has nothing to do with the ground. I actually never connected the ball and hitch. this has happen on two different trailers now. I have a pop-up that didn't have running lights. I assumed it was the pop-up. (just bought it used). now I hooked up my utility trailer and no running light either. I have no power at the Envoy 7-pin plug for running lights. It has to be the plug !! Right ??
Well, it could be the plug, adapter, fuse, other connection. You need to check the running light pin on your 7-wire plug first. If the signal's not there, then look backwards into the car. If it is, then it's clearly the 7->4 adapter or something in the trailer.

What kind of voltage should I be getting at the plug. if I am touching the ground and stop lights with a volt meter. and I hit the brakes, what should the volt meter read or do ??
It'll read 12V. The only signal that comes out of the 7 pin connector that's other than 12V or zero is the brake controller output, which is a proportional signal that can be anywhere in between. However, it's not always pure DC, which is easy to measure on a meter. The Tekonsha Prodigy and many other modern controllers are switch-mode, meaning they switch from zero to 12 volts at a high rate of speed, and the proportion of time spent at zero versus 12V is what causes the brakes to be harder on or off as the controller commands them to be. You can see this operation with an oscilloscope, but that's not a normal garage tool.
 

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Discussion Starter #7
Sounds fun to find !!!! :crazy: Why don't you drive up to East Greenville and give me a hand.. I just sold my wife's treadmill to someone in Villanova.. Thanks for the info, I will check out all the fuses.. :confused:

Thanks
Jason


Blulytes said:
It is a fuse issue...
I forgot which one it is, but it is poorly labeled and not easy to find....

I had the same thing happen to mine...
 

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Discussion Starter #8
the roadie:
Definitly knew the AUX. & brake's didn't run through the adapter. All that makes it through is running lights, left brake&turn, right brake&turn , & ground.

There is nothing at the 7-pin plug. So my next step is to work backwards to find the issue. I will be looking for 12v somewhere along the line...

thanks
Jason
 

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You may be right if there is no voltage at the pug. There are fuses under the hood for right and left trailer lights. I blew one of each for some reason until I fixed the ground. I checked mine with a 12volt test light but I also have 4 wire plug with led's that plugs in and will light up for each function. I may have bought it at Wally world. It is a Hoppy product. Very cheap.
 

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OK, the front wire that is disconnected by the underhood fusebox is used for a constant +12V only!


I had this problem with my TB two years ago, this is how you fix it:

Open the underseat fusebox (not the underhood one, the underseat one) and check fuse #42. It will be labeled TR PARK for trailer parking lights.

That should be the burnt fuse, replace with the proper amp fuse from the end of the fusebox where the extra fuses are stored and voila!
 

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Discussion Starter #11
ScarabEpic22 said:
OK, the front wire that is disconnected by the underhood fusebox is used for a constant +12V only!


I had this problem with my TB two years ago, this is how you fix it:

Open the underseat fusebox (not the underhood one, the underseat one) and check fuse #42. It will be labeled TR PARK for trailer parking lights.

That should be the burnt fuse, replace with the proper amp fuse from the end of the fusebox where the extra fuses are stored and voila!

#42 it was.. It took me 4 tries to locate it thought. drivers seat, nope, passenger seat, nope, behind passenger seat, nope, behind drivers seat, bingo.. I just gotta hit the auto store for some fuses....
thanks ScarabEpic22 for pin pointing the problem.

Thanks to bullethole, the roadie, Blulytes, Envoy Fan for assiting me with this issue.

Thanks
Jason
 

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jgray_22 said:
#42 it was.. It took me 4 tries to locate it thought. drivers seat, nope, passenger seat, nope, behind passenger seat, nope, behind drivers seat, bingo.. I just gotta hit the auto store for some fuses....
thanks ScarabEpic22 for pin pointing the problem.

Thanks to bullethole, the roadie, Blulytes, Envoy Fan for assiting me with this issue.

Thanks
Jason
Glad we can help, everyone (including me) forgets the underseat fusebox. What gets me is that all of the trailer functions except the running lights is underhood.:weird:
 

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Many thanks

My thanks to you guys. I was about to pull my hair out with this one. I borrowed a friend's boat that I had towed with their Silverado many times. When I went to return it, I realized that only the left side lights were working on the trailer and none of the right or running lights were working. I assumed it was something wrong with my TB (bought it used with 19k on it...it's an '03 with 31k now). I checked the fuses and sure enough #42 was out...also, another one was out under the hood. The folks who traded it in apparently swiped the spare fuses & the fuse puller.

Thanks again.
 

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I wanted to bring this thread back to life ... wow, 9/06 ... anyway, I had a similar problem, I got a 7-4 adapter and it had built in led lights underneath the pins so that you could see if the wiring was working. when I plugged in the adapter (by itself) and then hit the hazard lights, sure enough the left and right brake indicator leds on the adapter flashed fine ... however, I hook the trailer up and I dont get anything! so i just assumed the trailer lights were bad and i didnt really care because it was day time and you could easily see the tail lights on the tb ... so, at the end of the day, I go to lock my tb with the keyless remote and what do you know, the trailer brake lights flash with the headlights and taillights when I hit the lock button on my remote ... now I thought that was pretty strange ... any ideas? (besides checking the ground and the fuses) is there any chance that I got the wrong adapter? but the leds on the adapter worked? im confused ... thanks in advance
 

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Do a search by my username, I just had to replace my entire truck plug because it was corroded from the back side. The pins corroded right off! I guess moisture got into the plug and puddled. My TB has seen salt roads only a couple times and had only about 10k miles on it at the time!

Edit: Here's a link to the thread

http://forums.trailvoy.com/showthread.php?t=24027&highlight=plug+corrosion
 

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thanks for the replies guys, but what I'm stuck on is how are the led indicator lights on my 7to4 adapter flashing? and not my trailer lights? (and I know they lights themselves are good because when I hit the lock button they flash :weird: ) it blows my mind...
 

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Sounds to me like the wiring on the trailer has the problem. Keep in mind that just because the trailer lights flash with the lock function doesn't mean the running, brake and blinker functions are wired up correctly.
 

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Sounds to me like the wiring on the trailer has the problem. Keep in mind that just because the trailer lights flash with the lock function doesn't mean the running, brake and blinker functions are wired up correctly.
i'll check the wiring when I get some time ... thanks for all the replies guys!
 

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trailer light woes

Without a trailer all of my lights seem to work properly. When I connect a trailer, the trailer lights work fine during the day without the vehicl lights on. Once I turn on the car lights things get squirly. Depressing the brake makes all of the lights go out. Turn on any turn signal and both left and right signals alternatively flash. I have checked the receptacle ground on the car and it seems good and the trailer works fine on other vehicles. All fuses appear to be fine. What do I check next????
 
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