Using LEDs in the front fender side-markers on a Jeep Wrangler TJ

machoheadgames said:

You need to evaluate how they operate both with headlights on and off. Front turn signals and side markers blink in unison with headlights off. They alternate when headlights are on. You also might have a problem in one situation but not the other due to the power flow through the LEDs only traveling one direction.

In other words, flashing out of sequence is not necessarily significant, but I’m not sure you’ve noted all conditions to make sure everything works all the time. I have never seen 100% LEDs work in all situations without the diode/resistor mod.

Click to expand...

Josey82 said:

So I stepped outside to run everything through the conditions you mentioned.

With the headlights/running lights completely off the side markers don’t illuminate at all. The front & rear signals flash in unison when using the turn signals and hazards, but nothing from the side markers at all.

Once I turn on the running lights, all lights illuminate properly including the side markers. The front and rear signals flash in unison when using the turn signals and hazards, but the side markers flash out of unison from the others when using both the turn signals and hazards.

The side markers react the same way as above once the headlights are fully switched on in both the high beam and low beam settings of the headlights.

Does that help you diagnose any better? I’m not certain if those conditions are the way the side markers are supposed to perform even with the incandescent bulbs?

Click to expand...

machoheadgames said:

Interesting. Most of that is normal behavior, the one thing malfunctioning is the side markers not working as a turn signal when the lights are off. That is almost certainly due to the bulbs chosen not having a rectifier in them that allows the current and ground to work on either side of the bulb, making the bulbs (non polar). If you flipped the side marker bulbs in their spots then you would likely flip the behavior where they would blink properly with headlights off but wouldn't do anything with headlights on. Most likely, anyways.

What's weird is that your side markers work at all with LEDs in the front turn signal locations. The factory design basically forces the side markers to rely on the front bulbs being actual incandescent bulbs in order to ground properly. The side markers ground through the unused filament which is why the setup is called floating ground.

Maybe there is something special with your front turn signal bulbs that allows the ground current to still travel through the front bulbs as stock intended.

My next step would be to try a non polar LED (one that functions no matter what orientation it sits in the socket) and see if everything works then. If so, you're good to go. If not, you need the diode/resistor mod.

Alternatively, the diode/resistor mod would fix your issue and keep the bulbs you got. So the bottom line is that you may be able to fix the issue with different side markers, but the diode/resistor mod should take care of it for sure.

Click to expand...

Josey82 said:

Thanks Macho. I'll flip the side marker bulbs 180° in their sockets just to see if there's any change in the performance, but if I'm not mistaken, one of the features that separates the Sylvania "ZEVO" LEDs from the regular line of Sylvania LEDs, is that the ZEVOs have a reverse polarity or rather a completely non-polarity design. The ZEVO LEDs are a bit more expensive but I decided to stick with them in every application rather than mix and match with the regular Sylvania LEDs.

Sounds like the diode/resistor wiring mod for the side markers is what's next on the list for me. I like the idea of the in-line patch cables like Nightshade created and showed earlier in this thread, rather than cutting and splicing into the original wiring. That's a pretty genius idea in order to keep everything original and easliy reversible.

Click to expand...

Zorba said:

I'm not sure I'm reading this correctly - but the front side markers are designed to flash opposite of the main turn signals. That's why replacing the front bulbs is so problematic. What am I missing?

Click to expand...

machoheadgames said:

No, the turn signals and side markers flashing opposite is just a byproduct of the design. They wanted to use a 2-wire incandescent bulb to do two functions: be a side marker and blink as a turn signal.

The way they accomplished that was with a floating ground setup. The front turn signal bulb has three wires (bright, dim, and ground), so it already has both the parking light circuit and the turn signal circuit available. Instead of giving the side marker its own dedicated ground, one side of the side marker is connected to the parking light circuit and the other side is connected to the turn signal circuit.

When the parking lights are on and the turn signal is off, the turn signal filament provides a path to ground through the inactive filament, so the side marker lights normally. When the turn signal flashes on, both sides of the side marker are at battery voltage, so there’s no voltage difference across it and it goes out. When the turn signal turns back off, the voltage difference returns and the side marker lights again. That’s why it flashes opposite the front turn signal.

It’s simply an elegant way to get two functions out of a 2-wire bulb without adding another ground wire or more complicated electronics.

The downside is that replacing the front incandescent turn signal bulb with an LED removes the filament that was acting as the return path. Since the side marker depends on that path to complete its circuit, it often stops working correctly. That’s why the diode/resistor modification exists—it recreates the current path that the incandescent filament used to provide so the side marker continues to operate normally.

Click to expand...

Zorba said:

I'm aware of this - I'm not sure the OP is. Or I'm just out to lunch and missing something else?

Click to expand...

machoheadgames said:

OPs lamps are not working in certain conditions because he installed LEDs and he was wondering if he needs the known fix for his situation or not.

Click to expand...

Zorba said:

I got that too - what I "got" was he kept saying his front side markers were flashing "out of sequence" with the main flashers - which is what they're designed to do.

Click to expand...

machoheadgames said:

Yes, out of context that specific behavior is fine because stock does it. Doesn’t change that he still has a problem though. It’s just not the exact thing he thought was a problem that is the actual problem.

Click to expand...

machoheadgames said:

Yes, out of context that specific behavior is fine because stock does it. Doesn’t change that he still has a problem though. It’s just not the exact thing he thought was a problem that is the actual problem.

Click to expand...

Josey82 said:

So what is my problem? Lol.

I’m guessing it’s that my side markers don’t illuminate unless the lights are switched on?

Click to expand...