vert

2003 C320 sedan. Both front blinker/turn indicator lights were going in and out for a while. Fixed both by hardwiring per TSB P-B-82.10/195f. Passenger side still works fine but driver side stopped working shortly after the fix. Tested the actual signal wire and there's no voltage on it while hazards are on. This is different than before the hardwire fix since at I had power on that wire and it was just a faulty bulb holder as per TSB. Again, it worked fine for a while after the hardwire fix but now there's no power at all.

How would I go about troubleshooting this one? Could be a break in the driver side signal wire and I thought I can tap into it somewhere else, but no idea where to start. Or is there something else I need to be doing to fix this?

slammer111

Check the wire sand what it goes into. I'd also check the voltage at the part that the where the wire connects to the SAM.

vert

The wire from the driver side turn signal is routed along the fender and then disappears under the brake fluid reservoir. Could someone please tell me exactly where I can find this wire's starting point? There's a fuse box on the driver side next to the brake fluid reservoir but the wire loom doesn't seem to go into that box. There's no fuse for the turn signals either, according to the fuse diagram. It just stated that it's electronically controlled.

KevinH2000

I had the same problem a few years ago and I was unable to find a way to trace the wire. This link shows the steps I took to resolve the problem.

The component you described as the fuse box on the driver's side is actually the front Signal Acquisition and Activation Module or "Front SAM." I had to replace my front SAM to repair the blinker. I hope your problem is easier and less expensive to repair.

Good luck.

vert

Wow, what a great writeup you have describing and finally solving your turn signal problem. It certainly does sound the same to what I'm experiencing.

Before I got down the same road of buying a new SAM part number 2039060005 from FCP Euro, I was wondering.... Do you think I could make the front driver side turn signal work by splicing it into the driver side outside mirror or the rear turn signal? If so, how can I locate those wires to try?

KevinH2000

I don't know enough about the system to say for sure. My experience is that Mercedes seems to make everything twice as complicated as it needs to be. I would have assumed that the turn signals and hazard lights operated as simple switches that turned on a flasher unit that in turn operated the light bulbs in the turn signals and the outside mirrors. This is apparently not the case. The turn signal lever and hazard button appear to send a signal over the CAN Bus to the Front SAM which tells the front SAM when and how to operates the bulbs.

Another possible issue affecting your proposed solutions may be the fundamental difference between LEDs and light bulbs. On my car, the mirror lights are LEDs. Because LEDs require less voltage than light bulbs, the amount of voltage the Front SAM sends to the mirror LEDs may not be enough to operate a light bulb. So, if you figured out which wire to tap, it may not have enough juice to illuminate a bulb.

vert

Update:

Interesting development today. I tried a redneck method of fixing the front blinker problem. Connected a long wire into the rear blinker harness and then temporarily ran it to the front of the car on the outside, connecting it to the front blinker. That "fixed" the problem and both front and rear blinkers worked correctly. The dashboard reported two non-working blinker lights and the signal stalk was clicking fast indicating the same issue. At this point I was going to just splice the front blinker into the rear and live with the error messages and the fast indicator sound from the stalk, or try to figure out how to disable that. I just need it to work for safety and to be able to pass the state inspection.

Before doing that I decided to wire up the front blinker correctly as intended and somehow it started working again. No error message on the display and the correct speed sound from the indicator stalk. I have no idea how tapping into the rear blinker jumpstarted the front but if it actually stays working I'll be very happy.

KevinH2000

Congratulations on your persistence and creativity. I expect that it would require a person with expert-level knowledge of the circuits involved to explain why you were able to fix the problem using this method. I guess I need to take a "think outside of the box" approach when it comes to future problems with my car.

C230 Sport Coup

If the computer sees a short it will kill the power to the bulb, so thats something you could have checked with a scanner if you didn't,
both live data, and history.

vert

I just have a generic OBD scanner which wouldn't show this info. But good to know for the future.