Flasher-Turn Signal Relay diagnosis: 1985 300D
 

About a year ago, I noticed that when I used my turn signals, they were operating incorrectly:
Left/right dashboard indicator flashing rapidly.
Or sometimes...
Left/right dashboard indicator not flashing and instead staying constantly illuminated.

I checked each turn signal bulb in the front and rear and confirmed all were operating correctly. Even swapped with new bulbs, tried the turn signals, and the incorrect operation continued.

I have removed and opened the flasher-turn signal relay (pic 1 and pic 2) and tested it. Pic 3 shows me using a grounded test light on pin 49a and the notation shows what happens (very rapid vibration and audible buzzing). My guess (perhaps someone who knows can confirm or repudiate this):
The relay is not supposed to rapidly vibrate and buzz loudly. Stated another way: The copper plate that moves/vibrates should be a slower and more syncopated click-click-click-click as one would expect for a turn signal relay. Yes or no?

Given the current operation of the relay, perhaps it has failed? It is stamped "4/85" on the outside so it has seen a lot of years of work.

I'd appreciate any insight on this little situation. Thanks-

What happens if you leave the turn signals alone but apply the emergency flasher?

When I had what I thought was a turn signal relay issue after turning on and running them a bit the emergency flasher the turn signals would work for a while, and I would repeat that till finally the turn signals stopped all together.

Because it worked after using the emergency flasher switch, I made a best guess that there was something in that switch causing the issue. In any event replacing the emergency flasher switch fixed the issue. Apparently, some of the turn signal circuit runs through the emergency flasher.

What happened to the emergency flasher switch? My wife thumps her purse down on that part of the counsel. I think years of that finished the switch off.

Note I think some generic turn signal flashers would work (if you pick the right amperage) but you cannot easily test that due to the Mercedes flasher relay having round pins and the connector being setup for round pins.

In my 240 and on the 300 I'm currently playing with: The hazard switch has been a problem every time. If I activate the hazards and push too "hard" downward, the relay will buzz like the door buzzer. Turning off and turning the hazards back on more lightly has the hazards work like normal.

I'm with Diesel911 on the hazard switch needing some troubleshooting. On the 240, the switch would like to sit in a "not on not off" mode. In this mode, the turn signal stalk did diddly. Hazards would not be currently on. If I jiggled the hazard switch, everything would be back to normal.

All 4 external turn signals stay constantly illuminated. Same for the 2 indicators in the instrument cluster.

Indeed. The FSM "Electrical Troubleshooting Manual" has detailed schematics which proved useful as I worked this matter. Though quite predictably, the relay is referenced only as "SOLID STATE".

So far, the hazard switch does not appear to be the source of the problem.

Thanks for the replies.

Current status:
The relay's polarized electrolytic capacitor has failed. What a surprise after 37+ years! I'm seeking a suitable replacement.

Hmmm, good to know that there is a cap in there to go bad. Looking at the picture, looks like on on the tach cluster I just replaced.

When my hazards stop buzzing and stop working, I'll know where to look now!

I am an info magnet and I could not stand not having a decent manual for my Mercedes bedause I know much money can be saved if you have a good manual.

I have long had the CD manual and later bought the paper manuals. Unfortunately, I cannot remember the exact details of my own turn signal failures. I took a chance on the hazard switch being the issue because it was cheaper compared to, they turn signal relay. I believe I bought a Hyco switch.

Never done much replacing or testing of circuits.