LED Brake/Blinker Bulbs Kills Blinkers??

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I bought a set (4) of 3157-CK bulbs from superbrightleds.com... Their lumen values were really high, so on paper these should have been a very good replacement for stock bulbs, AND they are only $10 per bulbs.

So I installed them tonight. Their dim mode looks like it's completely on par with the incandescent's dim mode. Their bright mode looks like it's not as bright. I haven't decided if I want to keep them or not, I haven't had to make that choice, because somehow they kill my blinkers!

So with all four of these red 3157's installed: Whenever my tail lights are on, the blinkers/hazards do not work. And inside on the dash, the blinker indicators (green arrows) remain dimly lit all the time.

Turn off the tail lights and the blinkers work normally.

They are not CAN bus bulbs as far as I can tell (see for yourself), and I am even using an LED compatible electronic flasher in place of the factory flasher.

My dash with my tail lights on, and my blinkers and flashers off:
O35p9I6.jpg


I emailed SBL but I'm sure they're just going to tell me to return them. I figured I'd post the problem here too in case there's some other known issue that is causing this? I was so excited to FINALLY have good working red 3157's.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
:undecided: What happens if you pull the front 194 bulbs from the corners, do your rear turns still act up and the cluster stay lit? It sounds like the parking lights are back feeding into the turn signals.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I'll have to try that another day, I've already put everything back together.
The 194's and the 3157's in the front are all LED already, FYI.

How would this 'backfeeding' happen?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
:wink: I know, I had a similar issue when I put LED 194 bulbs in.

Edit: The 194 bulbs don't have a dedicated ground, the parking light and turn signal use each other as a ground. Due to the lower resistance of the LED, a little bit of current leaks through the entire system, and is enough to light up the other bulbs.

If you flip the 194 bulbs around, the problem will change. When you activate the turn signal on one side, the parking light on the other will flash along with it.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
So is there a solution to this problem? I'm still not understanding what's causing it but I've never read that it's "impossible" go to all LED on TB exterior lights. So there must be SOME solution to this, yeah?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
There is, essentially you have to add your own dedicated ground, making it a 3 connection circuit instead of just 2. Before places sold switchback modules, I had to design my own, so that's one step you can leap frog.

You'll either have to splice into your stock wiring for this, or buy expensive connectors to go between the 194 harness and the 194 bulb holder in the corners. So you're either spending time, or a decent bit of money, to get this mod done and behaving properly.
 
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gpking

Member
Dec 27, 2013
534
Berkeley Springs, WV
Hold on, all 4 of the bulbs are CK 3157's?
Only the brake/tail socket (and the front turn socket) are CK. The rear turn signal sockets are non-CK. That is probably your issue.
The only time I had weird behavior like that is when I put non-CK bulbs in the CK sockets (and vise versa).

I'm all LED with no issues.

Also, you should install a resistor on the tail circuit or you might lose cruise control.

You should only need to add a ground to the front 194 sockets if you replace them with LED. Mine caused backfeeding.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
There is, essentially you have to add your own dedicated ground, making it a 3 connection circuit instead of just 2. Before places sold switchback modules, I had to design my own, so that's one step you can leap frog.

You'll either have to splice into your stock wiring for this, or buy expensive connectors to go between the 194 harness and the 194 bulb holder in the corners. So you're either spending time, or a decent bit of money, to get this mod done and behaving properly.

So grounding the 194's is all I need to do? That's not too bad. As a test, removing those little 194's should also (temporarily) solve the problem too then right? I still haven't decided if I want to keep these red 3157's so I'd like to test them more before I'll have time to get around to the 194 wiring mod.

Hold on, all of 4 the bulbs are CK 3157's?
Only the brake/tail socket (and the front turn socket) are CK. The rear turn signal sockets are non-CK. That is probably your issue.
The only time I had weird behavior like that is when I put non-CK bulbs in the CK sockets (and vise versa).

I'm all LED with no issues.

Also, you should install a resistor on the tail circuit or you might lose cruise control.

You should only need to add a ground to the front 194 sockets if you replace them with LED. Mine caused backfeeding.

Yeah all 4 of my reds are CK, and my front ambers are non-CK. Mine's a 2008.
I replaced the 194's with LEDs very early on but only have issues with this when I put LEDs in the rear, oddly enough. With regular bulbs in the rear, the front LEDs work totally normally. *shrug*
 
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Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Please use the multi quote feature when replying to multiple posts, to avoid double posting :popo:

MultiQuote.jpg
 

Matt

Member
Dec 2, 2011
4,019
There is, essentially you have to add your own dedicated ground, making it a 3 connection circuit instead of just 2. Before places sold switchback modules, I had to design my own, so that's one step you can leap frog.

You'll either have to splice into your stock wiring for this, or buy expensive connectors to go between the 194 harness and the 194 bulb holder in the corners. So you're either spending time, or a decent bit of money, to get this mod done and behaving properly.

@Blckshdw Can you throw me a bone on how to do this? I'm getting sick of looking at my indicator lights on the dash illuminating when the lights are on.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
@Blckshdw Can you throw me a bone on how to do this? I'm getting sick of looking at my indicator lights on the dash illuminating when the lights are on.

Quickest and easiest method would be to buy a pair of ready-made switchback modules. I believe prices on those have come down considerably from when they first came on the scene. You'll have 3 connections on the input side (park, turn and ground) and 2 on the output side (park and turn). I used the fender grounds for mine.

All you'll need to do is either splice into your wiring, or get some connectors/pigtails to make an extension piece. The first time I did the 194 mod, I bought the Delphi connectors. Pricey... This second time I bought some empty 194 bulb bases to plug into the factory socket, ran those inputs to the module and bought some 194 socket pigtails that could twist lock into our headlights (slight mod with a razor blade was needed)

That's pretty much it. Just have to determine what components you want to use.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
So does anyone have maybe a drawing or something of exactly what you need to do here. This thread is old and the red LEDs have actually been sitting in a box on the floor in my truck for years now. The textual description of this mod doesn't do it for me, I just don't understand it. But I would like to do it.

I also don't know if I ever got around to pulling my 194's and trying the red's again, I should give that a shot at some point.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
I didn't make a sketch of the one I made. THe link I used, that had the schematic is gone. But if you do a google images search for "type 2 switchback schematic" you'll see a number of ways to do this mod. Just have to pick one that looks like a comfortable match for your skill set
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Is a simpler solution to this problem to simply snip the 194s, and splice them into the 3157's in parallel. Then they would blink in sync, instead of alternating, but it would remove the 194's from the picture?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Well the problem with that is the 3157 is a 3 connection circuit, and the 194 is a 2 connection circuit, so you can't make a simple connection like that. I found my old photoshop file, so maybe this will help...

Using a DPDT relay, you can make a polarity changer, which is what you need for the 194 bulbs, since whichever color is not being used, its + contact becomes the ground for the color that's active. So you'd use 3 diodes to prevent back feeding. Pins 11 and 8 would be connected together, as well as to the parking light contact of the 194 bulb. Pins 6 and 9 connected in the same fashion to the turn signal contact of the bulb. That covers your outputs.

For the inputs, the parking light signal from the truck goes to pin 13. That makes pin 11 hot, and sends the signal out to the parking light contact of your bulb. Pin 6 is treated as ground for the bulb, which is why pin 4 is connected to (fender) ground. This would be your normal state.

The turn signal from the truck comes in at pin 16, which activates the relay and flops both of the armatures, changing the polarity of your circuit. The diode from pin 16 to 13 will make sure the bulb gets power, in case it's daytime and your parking lights aren't on. So power will go through pin 9, to the turn signal side of the bulb, and pin 8 is the ground, exiting at pin 4. The diodes coming off pins 1 and 4, make sure your turn signal doesn't back feed through the parking light and cause the other side to flash in sync. At this point, you'll have the old Type 1 switchback, where the colors will alternate. :suicide:
I'm not entirely sure how to make it a Type 2 from here. I know you'd want to have a capacitor across the relay coil, to keep it engaged on the turn signal mode, but not sure exactly how to interrupt the parking light signal, so you'd actually get the flashing...


194 Switchback Polarity Module.jpg
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
:undecided: I had to go back and read all the old posts... A simpler option would be to snip the parking light wire feeding the front 194 bulbs, and taping off the truck side pieces. Extend the bulb side pieces to the fender ground. This effectively makes your 194s turn signal only, and gets rid of the back feeding issue. Would that work for you?
 
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gpking

Member
Dec 27, 2013
534
Berkeley Springs, WV
So what you're telling me is, either LED tail lights or LED 194s, take my pick.
Yes, unless you want to add some additional wiring.
... snip the parking light wire feeding the front 194 bulbs, and taping off the truck side pieces. Extend the bulb side pieces to the fender ground. This effectively makes your 194s turn signal only, and gets rid of the back feeding issue.
Or...

What I did to solve this and retain both functions is to introduce a diode module on each side from a "towing diode kit" at about $5 a piece depending on where you find them.
https://www.amazon.com/dp/B0002Q81Y4/?tag=gmtnation-20

The original park and turn signal wires get connected to the "IN", the "OUT" runs to the anode side of the LED, then I added a ground wire between the fender and the cathode side of the LED.
The diode prevents backfeeding and essentially ORs the inputs.
t10diode.jpg

So they operate as turn signal during the day, and illuminate solid at night.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
That's seems simple enough. Although I clicked your link and they were $25 each not $5 each :/

Also, just to be doubly clear, all the LEDs act totally normally once those are installed, one on each of the front 194 side marker lights?
 

gpking

Member
Dec 27, 2013
534
Berkeley Springs, WV
That's seems simple enough. Although I clicked your link and they were $25 each not $5 each :/
That link is to a 4-pack. Only 2 are needed but I couldn't find less than 4 unfortunately.

Also, just to be doubly clear, all the LEDs act totally normally once those are installed, one on each of the front 194 side marker lights?
Well, assuming your lights worked normally before LED, yes. The diodes just stop the backfeeding between park and turn signal circuits which seems to be your only issue.
You can see that problem illustrated in the video I posted a while back with my left signal backfeeding to the right one:

If you've already remedied hyperflash and made sure you used the correct CK/non-CK bulbs, fixing the 194s is the only other issue. I think we covered all bases in this thread.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
That link is to a 4-pack. Only 2 are needed but I couldn't find less than 4 unfortunately.


Well, assuming your lights worked normally before LED, yes. The diodes just stop the backfeeding between park and turn signal circuits which seems to be your only issue.
You can see that problem illustrated in the video I posted a while back with my left signal backfeeding to the right one:

If you've already remedied hyperflash and made sure you used the correct CK/non-CK bulbs, fixing the 194s is the only other issue. I think we covered all bases in this thread.

Cool cool cool. Ok one last question, about those diode boxes. Once they're installed and looking more or less like the picture you took, how do you finish it off? I need it to be water resistant and not likely to unplug itself from vibration. Should I just go nuts and wrap the whole thing with tons of duct tape? Or something else?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
With the female spade connectors, they should fit pretty tight out of the box. If you want, you can take some pliers or vice grips, and give them a pinch to make them grab a bit tighter on the module's tabs. Just don't pinch em too hard, or you won't be able to insert the tabs in the first place :laugh:

You really shouldn't be seeing much water behind your headlight with normal road driving, but if you're really concerned, wrapping them in electrical tape won't hurt anything.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
When doing this kind of thing, do you guys solder the connectors on to the wires or just crimp them on?
Also if doing a lot of similar mods, do you ground each one individually to whatever is nearby, or do you connect all the grounds and do one big ground?

I just checked the Diode link above and in addition to all the $23 3rd party sellers, amazon had a set of 4 for only $13.55. Now that's a dealio! Ordered that and a soldering iron for $40. I really need to learn to do at least basic soldering for spliced connections.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
If you're connecting modules together, like this, using crimp connectors is fine. As for grounds, I look to use factory grounds if one is nearby.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
The original park and turn signal wires get connected to the "IN", the "OUT" runs to the anode side of the LED, then I added a ground wire between the fender and the cathode side of the LED.
The diode prevents backfeeding and essentially ORs the inputs.
View attachment 86928

I'll probably be doing this soon. So, seems like it definitely doesn't matter which 'in' goes to which feed wire. As far as the out and the ground, I imagine that doesn't matter either right?
Because if the LED light only worked with current in one direction, it would already not be functioning half the time?
But even so, I can just flip the bulb if needed, if it get "wired backwards"?

Also what does "factory grounds" mean exactly? (blckshdw)
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Also what does "factory grounds" mean exactly? (blckshdw)

Places where GM grounds out wires/harnesses/modules by design. The ones @gpking and I are talking about are on the sides of the inner fender. By the battery, and by the air filter cover, if you take a look, you'll see a ground wire attached to a washer, bolted to the fender wall. You can crimp a spade terminal to your wire, loosen those bolts, and connect your ground there. If you wanna be lazy, you could also strip back some of the wiring, and just wedge the wire between the bolt and body.

87926
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Another "one step forward, two steps back" kind of adventure.

I wired up the diodes tonight. It was a pain in the ass because the wire for the 194 bulbs is so crazy thin. Getting a connector on them was not easy. I bought some 16 gauge wire I used to ground to the grounding screws, that part was actually easy.

I wired up the first one and it worked just as it was supposed to. I wired up the second but the 194 wasn't coming on. I thought these LEDs were "bipolar" or whatever you call it (wouldn't they have to be to work the way the default wiring is set up?) But I figure let me pull the bulb anyway and flip it because the connection I made look fine. I pull the bulb out and the pins rip out of the bulb and stay in the socket. Yay chinese garbage leds from superbrightleds. So I have to order a new one of those, but either way the LED rears should work now.

So I installed the four 3157 CK LEDs I've had in a box on the floor of my truck for 2 years now. These are probably the 4th set I've tried. There's always a brightness issues (aside from the CK issues). Usually it's that the bulb's dim mode is ok but the bright mode isn't bright enough. Well these bulbs are kind of the opposite. Bright mode is wicked bright, way brighter than a stock brake light. But the dim mode is also extra bright. Almost as bright as normal brake lights. So it kind of looks like I always have my brakes on when I'm driving.

Between this trailblazer and my previous S10, it really seems impossible to find 3157 LED bulbs that have acceptable brightness in their dim mode and bright mode. I need to drive someone elses car, and follow my truck around while someone else drives it, to see if these bulbs are good enough to keep or if I need to replace them. They are rated for 30 lumens dim and 110 lumens bright. They look more like 80 / 110. Ugh shit never ends.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Although to be clear, the diodes did fix the problem they were supposed to fix. And they are likely the easiest way to fix that problem. So that part of the process was good. A pain to wire but good otherwise.
 

Matt

Member
Dec 2, 2011
4,019
Between this trailblazer and my previous S10, it really seems impossible to find 3157 LED bulbs that have acceptable brightness in their dim mode and bright mode.

@DFWWIZ sells LEDs for our trucks. I have them as brake and running lights and they are plenty bright in "low" and "high" mode. Not sure if you can get a hold of him here, but you can get him on one of the TB facebook pages under Kevin Hanson.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
So I was driving to work today and my cruise control wouldn't turn on. What do you suppose is up with that?

LED bulbs in the brake light sockets. The reduced resistance due to the technology, is read by the BCM as the bulbs being burnt out, and as a safety precaution (assumed) doesn't allow CC to engage.

This used to come up a lot with discussion about load resistors vs the LM487 flasher relay mod. The newer LM486 (yes the number sequencing seems backwards) was supposed to address that. Or you can tap a pair of load resistors into the brake light wiring in the rear, that will also fix it.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I'll have to see what flasher module I have, I thought I had the good one but I guess not. But I hate upgrading to LEDs then adding resistors to just burn off the extra power you are saving.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Ok I've got a problem. And it's a stupid problem because I had it out just a few days about. But I spend about 20 minutes trying to remove the socket for the front amber 194 bulb to replace it, and i could NOT get that socked out of the headlight enclosure. You're supposed to turn it 1/4 turn or so then it pops right out. I turned that thing all the way around several times, and pulled hard at every possible rotation and it would not budge. In fact it even started to crack and break the plastic that makes up the plug/socket. But the thing would NOT come lose.

Is there some trick to this?
 

Matt

Member
Dec 2, 2011
4,019
There's no trick, I would assume that the right tabs are not lining up with the right slots. Mine practically fall out.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
One of the tabs is larger for proper orientation. Maybe just have to keep going around and try every possible position.
 
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