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2002 chevy trailblazer_ltz
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170 Posts
Discussion Starter #1
Hey everyone, I have a semi-major issue. This evening, I hooked up two reverse facing fog lights, powered by the 12v power source in the rear of my TB from the cigarette lighter receptacle. This worked great because I had it powered through a fuse, which connected to an on/off switch provided with the fogs. I got stupid (and greedy) though, and decided that it would be nice to have them flip on with the reverse lights as well, so I tapped into the center wire on the tail light socket (on with the reverse lights) with the wire between the switch and the fogs so that it wouldn't be connected to the 12v power source without the switch being on, and it would still come on with the reverse lights. I tested it, and it seemed to be working great. I took it out for a drive afterwards and when I hit unlock, all of the rear lights (both reverse, and both fogs) flashed on and off like normal, and since I was just driving a few houses down, I switched the lights on and was going to drive with them on just to see what sort of rear facing light I'd get on trails, roads, etc. if I were to leave the fogs on and when I got to where I was going, I switched them off and everything was fine, except that my 4WD indicator light would only come on if I was in reverse. This wasn't a big deal I thought and I could live with that if it meant having those lights, but when I came back out to my TB, I hit unlock and though I didn't see the lights flash in the rear with my unlock, I got in and started it, and noticed that now even in reverse the 4WD indicator light didn't light up. So, I stopped and put it in reverse, but none of the lights lit up. Put it in park, and switched on the lights manually and all four lights lit up. Turned them back off, drove home and pulled back into the garage and decided that I needed to unhook the reverse lights and that if I wanted them on, I could just switch them on when I was backing up. I cut out the wire that I had attached to the reverse lights, to where now I just have the reverse fogs hooked up to the 12V power source through a fuse, then to a switch, then straight to the fogs and they work just fine when I turn the switch on, and they turn off when I turn the switch off, with no connection to the reverse lights what-so-ever. I also reattached my reverse light wires to how they were originally, but unfortunately, I still have no reverse lights while in reverse or when hitting unlock on my keyfob, and I have no 4WD indicator light.

PLEASE HELP! I have no idea what I did. I thought immediately that it might be a fuse, but they still worked, just not when I wanted them to. Unless maybe my fog lights were just being powered by the 12V source and it blew the fuse that leads to the fogs as intended by the factory. But what connection does that have to the 4WD indicator light? Thoughts? Suggestions? I could use the help.

And yes, I realize I'm an idiot for trying to take that shortcut. :duh:

Thanks in advance.
 

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2004 gmc envoy_slt_xl
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123 Posts
well i had the sam idea but i decided to use the trailer plug(7 prong). i used an adaptor to cut it down to a 5 wire and used the blue wire on the 5 prong to turn the rear lights on. It works good. Now for your problem make sure that you did not create a short in the wireing on the rear of the vehicle. second if you can not locate a short then check the fuses again.
 

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2005 chevy
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6,469 Posts
Do you have a volt meter? First thing I would do is check the fuse (#27 in the front block I think), to see if it's blown. If it looks OK, put a meter on it to make sure you're getting continuity, then also measure at the reverse wires where you spliced in for the lights.

The added load may have been too much for the fuse, or if you didn't wire it properly, you could have shorted something. Your idea can work, you may want to introduce some relays into your system, like in this article :coffee

Installing Auxilary Backup Lights
 

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2004 gmc
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26,181 Posts
Without a relay or a couple of diodes, you can't just short functions together like that with a regular switch. What you need is a "single pole, double throw" switch. And a bit of reading about how electrical things work, or an experienced buddy, is critical. You could really burn up some expensive stuff in our computerized vehicles by guessing. :nono:

Check rear fuse block #32. The vehicle backup lamp circuit is run through the BCM so it will have that "flash for unlock" feature. I bet the added load of the fogs blew that one.

A better place to tie them in with less risk is the trailer backup lamp feed, a light green wire at the trailer connector. It's protected by front fuse #27 AND then front fuse #4. This circuit also won't flash when you unlock the vehicle.
 

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2002 chevy trailblazer_ltz
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170 Posts
Discussion Starter #5 (Edited)
:worried: I definitely need to learn to ask first, and install later (or at least run a search here on similar installs).

Thank you SO much for your help. I'm at work right now, but after I get off in about an hour I'll be checking those fuses in the parking lot and then hopefully heading to the parts store to get the replacements for an easy fix.

I did some more reading, and thanks to another incredibly helpful post from Bill, I believe I've found the fix to my indicator light issue as well, but I wanted to throw up my idea here and see if it holds water. I found that if the fog light button is still operational to turn on/off the fogs, but the indicator light doesn't come on, it's likely fuse #11. Roadie also suggested front relay #39. Fuses I can do and are simple. I'm just not sure how you would go about finding/replacing relays if it's not that fuse. Any help? I have a feeling this is going to be something simple that I should know, but after running a forum search and coming up with nothing, I thought it would be better to just ask first.

If fuse 11 or relay 39 happens to be the fix for my fog light indicator, should it also fix the 4WD indicator light? I've run searches on the 4WD light and for everyone else, their 4WD is messed up, so the results don't really help me. Mine all works just fine, and as far as I can tell, even my A4WD is kicking in properly (icy roads here in St. Louis at 3 am this morning), but the indicator doesn't light up. I can feel the 4WD engage/disengage and I could live with it not working, but in case of a failure in the drivetrain that would be indicated by that light acting up, I'd prefer it worked.

Again, I really appreciate all of the help and can't say thank you enough. Yet another example of why TrailVoy is priceless.
 

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2004 gmc
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26,181 Posts
Relays can only be diagnosed by two methods: swapping them with an identical neighbor, or troubleshooting them functionally with a meter. Except for the larger starter relay, all trailvoy relays have neighbors you can borrow for a short while.

Tell me more about your 4WD indicator lamp issue. I assume you mean the lights ON the rotary mode switch? Do they all light up together when you turn on the ignition during the lamp test?

4WD indicator lights and the fog lights are totally separate issues.
 

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2002 chevy trailblazer_ltz
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170 Posts
Discussion Starter #7
Well, the problems I had were:

1) Reverse lights didn't turn on. I lived with this, but I obviously needed to fix them as soon as possible.

2) My fog lights "on"/headlights "on" indicator wasn't working. They're the small green lights in the pictures below.



3) My 4WD indicator light wasn't working. When I tried starting the TB or selecting a new drivetrain (2WD, A4WD, 4 Hi, 4 Lo) no lights would come on. It's the small orange light in the photo below.



Thanks to roadie's advice on my post as well as on another thread here regarding fog light indicator lights not working, I was able to at least get started on my diagnosis and I knew I had to check Fuses 4, 11, and 27 in the front box (2 15A and a 10A if I'm not mistaken), and fuse 32 in the rear box (10A), so I started in the front box and none of the fuses were blown there, so I started to get frustrated, but when I checked fuse 32 in the rear, it was blown. I ran down to the parts store and bought all of the fuses to replace them all, just for good measure. However, I replaced fuse 32 in the parking lot and started my truck and I saw that the indicator lights were working. So, I got a little confused thinking that maybe fuse 32 was just to fix those, when what I really needed fixed was the reverse lights, but I shut the truck off, and put it in reverse, walked to the back to see if for some reason the reverse lights were on, and they were. That 10A fuse #32 fixed every issue I was having. I guess I just got really lucky and that tiny fuse kept my mistake from breaking anything else.

Thanks so much to everyone who commented (especially Roadie for having great advice all over this site). I still can't believe they're all working just from fixing one little fuse.

Those photos above were taken after I fixed it and was able to snap some. Just to finish this off, the success picture (LED reverse lights to match the LED license plate lights, as well as the new aux. lights)!

 

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2005 chevy
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6,469 Posts
Glad you got it working, and really glad it was something easy! Definitely need to change the wiring game plan :coffee, but what you're wanting to do is possible. :yes:
 
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