Hello everyone,
I have a somewhat “unusual” problem and hope that someone might have advice for me.

Initial situation: 1993 C4, slightly modified to be legally registered in Germany. Yellow parking lights at the front are not permitted in Germany. The 2-filament bulb was replaced with a white/yellow LED, and the turn signal relay was also replaced accordingly. However, the side marker bulbs were also removed, so they are no longer functional.
I would like to put the side markers back into operation. To do this, I first installed standard bulbs. As a result, the flashing is asynchronous with the LED front turn signal which is painful to watch (not alternating, just all over the place). When not flashing, the side marker works as it should. At the same time, I have a slight glow in the direction indicator on the dashboard when I activate the parking lights.

To fix the asynchronous flashing, I also installed LED bulbs in the side markers as a test. Unfortunately, the result is exactly the same – asynchronous flashing. The only difference is that the arrow in the dashboard remains completely dark, presumably due to the blocking effect for a reverse current.

I tried to find out what the cause could be and also looked at the circuit diagrams. Apparently, the ground connection of the side markers runs through the front turn signals. Replacing them with LEDs should result in different characteristics. Could a parallel load resistor be the solution here?

I am already considering simply connecting the side marker directly to the parking light and dispensing with the flashing function. However, I would then like to ensure that the correspondingly lower voltage (dimmed side marker) is applied. I am still unsure where I can best tap into this.

Do you have any suggestions? How did you resolve this situation while using LED blinkers?

In addition, I have noticed that on some models the turn signals flash simultaneously, while on others they flash in opposite directions. Does this have anything to do with the daytime running light (DRL)? I don't think I have this installed.





Any input is well appreciated.

Cheers,
Julian

 

Bumping this with new findings.

I installed a 8 Ohms 50W Load resistor in parallel to the blinker line right before the bulb between the blue and the black wire. Since the resistor gets hot when the blinker is engaged and stays cool with only the parking light on I can assure that contact is there and the resistor is installed at the right connection points.
However, it has absolutely no effect (besides additional heat.. ). The situation is exactly like before. I uploaded a short clip here:


Again I can rule out that the different switching time characteristic (LED turns on faster) does make any difference. Using LED Bulbs in the side marker looks exactly the same.

I still do not fully understand the electric circuit / GMs idea behind it. So here are my thoughts:
1. Since the parking light also was changed to LED and is somehow part of the system (actually I do not fully understand why the parking light turns off when the turn signal is engaged), it might be necessary to add another resistor parallel to the parking light?
2. I just tried installing the load resistor on one side (passenger side) because I do not want to damage more cables than necessary. As of now I don't see any reason why there should be any dependency between left and right.

Any Ideas?

edit: I just tried 1.) and installed another resistor parallel to the parking light. This setup should now fully simulate the classic 2-filament bulb. Absolutely no difference

 

Your lights are working as intended. The side marker grounds through the filament of the turn signal/ front parking light bulb. When the parking lights are on the side marker current goes to ground throught the turn signal filament. When the turn signal only is flashing the side marker grounds through parking light filament. When both the turn signal and the parking lights are on the side flashes out of sync with front bulb because it has 12v on both sides when the turn signal is lit and goes to ground when the tyrn signal is dark.

This sceme works because the side marker bulb is small compared to the other filaments. LED currents are different and upset the intended behavior.

 

Hey Pete,

thanks for your reply and sorry for the late answer.
You are right about the circuit - I did understand it by now, but still wasn't able to locate the problem. My question was, HOW the LED replacements behave, why the turn signals are completely all over the place and what can I do to solve this.

Meanwhile I found the solution.
The LED bulbs which were used at this time do have a delay on their own. I took them out of the sockets and tested them in the workshop. When 12V is applied, it takes about half a second until they light up. This explains the behavior and the "offset". I ordered another pair of white/yellow LED bulbs and luckily they light up right away with no delay at all. Actually they are a bit "faster" than the halogen from the side marker bulb - which is expected when comparing LED to halogen. Now everything is in sync (or perfectly out of sync when the park light is on). So my whole problem here was not based on the circuit but in a pretty weird behavior of the replacement bulbs.

I know this is a euro-thing and you guys in the us have not to worry about it, but replacing the stock turn signal light with an white/yellow LED is actually the easiest way to get the C4 legally on the road over here. Might be an interesting found that there are significant differences in those LED products.

Here is how it looks like now (white/yellow LED in the front, halogen side marker):


Cheers,
Julian