Strange LED Blinker Behavior

ChibbMD

ChibbMD

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Dec 29, 2021
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Dallas, TX
Quick review of my current blinker set up - I've got LED taillights in the rear (complete replacements) and LED bulbs in the front blinker locations. I've got electronic relays under the dash for both blinkers and hazards. Flash rate is perfect on all four corners whether I'm using my turn signals or hazards.

That said, I noticed something new recently. When the headlights are off (during the day) all the blinkers act perfectly. As mentioned, they all blink at the correct rate, and more importantly, they all blink completely. In other words, Blink-Off-Blink-Off.

Last night, driving with the headlights on, I noticed that they are blinking at the correct rate, but the fronts are not blinking completely. What I'm seeing is Blink-Dim-Blink-Dim. Makes it a bit confusing for other drivers to determine if you're really using your blinkers or not. Everything looks normal in the rear. No issue there.

I swapped out to different LED bulbs in front. Same problem. I tested this with turn signals and hazards (which have different relays), same problem. I tested with low beams and high beams. Same problem. My headlights are LED units (complete housing replacement, not just blubs). I'm a bit confused by any relation between turn signals and headlights. Any thoughts on what might be going on?
 
This isn’t new. The side markers rely on the front bulbs for ground. The front bulbs allow that in stock form. Put in LEDs up front and they stop allowing the side markers to work properly. The side markers then choke up the system. You can rewire the side markers to not depend on the front anymore, or go back to stock on all 4 front bulbs. The rear LEDs are fine and affect nothing as long as you have the proper flasher.

The headlights being led has nothing to do with it. The difference with headlights on or off once again is due to the side markers relying on the front circuits for power and ground which changes the way they are fed when the headlights are on vs off.
 
Interesting. I had no idea, but it makes sense after reading over your post a few times. As far as re-wiring the side markers, I have a couple quick questions. 1) If it's only a matter of their grounding, could I just ground them to the frame/body and not bother messing with a complete rewire? 2) If I did completely rewire them, would the easiest place be to tie them into the taillights, which come on when the parking lights or headlights are switched on?
 
No, the issue is that the side markers are a single filament (aka 2 wire, 1 brightness). The only way you can rewire them that simply would be to wire the side markers straight to the parking lamp or the turn signal circuit and forego the other function.

The way it works in stock form is one wire from the parking lamps and one wire from the turn signal circuit goes to the bulb. When headlights are off, the bulb gets power from the turn signal when it’s on and it grounds through the parking lamp wire by traveling through the front bulb to ground. Side marker blinks with the front in that case.

When headlights are turned on, the side markers get power from the parking lamps, and the side marker bulbs seek ground through the turn signal filament of the front bulbs instead. When you have the headlights on and turn on the turn signals, the side markers see 12V on both wires and end up going out, which creates a backwards blinking where they alternate blinking with the front because they are basically losing ground when the turn signal starts going.

The way to rewire the side markers is to convert them to an artificial 3 wire setup. You put a diode on each of the two wires going to the bulb, put a 1 watt resistor on the parking lamp wire (300-500ohms is usually decent) which dims the bulb on running lamp mode. You then splice those two wires to one wire going to the side marker socket. The diodes keep them from backfeeding each other. Then you run the second wire to just ground.

Essentially doing this operates the 2 wire single brightness bulb as a 3 wire with a full brightness mode for turn signals and an artificially dimmed brightness on normal parking lamp mode. When headlights are off, you’ll just see the blink on-off-on-off at full brightness, and then when you turn the headlights on, you’ll see the blinker go bright-dim-bright-dim etc.

Here’s a vid of mine after doing the mod. Here is a link to a good write up for it as well. Same deal on TJ’s so the work is the same on a YJ as well. Well worth it in my mind, I’ll never have an incandescent bulb YJ again. Except in the dash where I like them.

LED turn signal mod
 

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You’re in Dallas, I could probably help you do it sometime if that would be easier. It’s pretty easy though, just need diodes, resistors, and some time to wire it cleanly.
 
Thanks Macho. I'm going to read over that a few times and let it soak in a bit. I'm curious, are the side markers supposed to function as turn signals? Is that the how they originally worked with incandescent bulbs? Although I've always thought it would make sense for them to blink, mine have been solid/non-blinking lights for so long I've assumed that's just the way it was.
 
Yeah they are a turn signal and running lamp. Single brightness but they run at full brightness and blink off-on at full brightness. It’s an effective setup in stock form. The easy route with LEDs is to just turn it into a parking lamp but then you lose blink function so to me it’s a compromise. I like to do the rewire because it’s unique, effective, and no compromises.
 
Flyer58 said:
I miss having the local Radio Shack
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That's funny. I was kind of thinking the same thing when I went to look these up on Amazon. I was like darn, I'm going to have to wait 4 or 5 days to get this project knocked out when I could've just run over to a Radio Shack and been done with it.
 
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ChibbMD said:
I think we're cut from the same cloth. I'm going to have to do this now. Lol. Can you confirm that I'm looking at the right resistors and diodes?

Resistors - https://www.amazon.com/dp/B00HKSKBO0/?tag=yjforum-20

Diodes - https://www.amazon.com/dp/B00W17LOBO/?tag=yjforum-20
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The diodes look perfect, the resistors I’d buy a 1Watt kit so you can play around with the dimmed brightness. You may not like 330 ohms. Or you may, but better to buy a kit and experiment yourself. I run really bright bulbs so the 560ohm resistors work well for me.
 
Yeah, I wish radio shack was still around. I’m 26 so I was quite young when the closed it, but I do remember going there for basic things my dad needed, not diodes and resistors but other stuff. I think he bought a stereo for the house and some other things there. Anyways, now I’ve learned that they have all sorts of stuff I could use these days, and makes me wish they were back. Oh well. I pretty much use Amazon and Delcity for everything these days.
 
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So the blinkers still don't work I tried to check the wiring harness and it looked good the blinker cam is slightly broken but that shouldn't make them not work should it?
 
Thomas said:
So the blinkers still don't work I tried to check the wiring harness and it looked good the blinker cam is slightly broken but that shouldn't make them not work should it?
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If the turn signal switch is bad it could be shorting the turn signal to ground.

Does it pop the fuse if you do a left or a right turn? How about if you turn on hazards? You may have to fry some fuses as an experiment to figure it out.
 
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