I've had recurring problems with the turn signals on the w115, and haven't seen a lot of resources online. I just learned something, so I thought I'd share. Feel free to chime in if you have more info on this topic.


The issue is the signal speed. They will work fine, then one day be super fast. It can be an intermittent problem, but it gets worse with time then stays super fast. It acts like you have a bulb out, but they are all working. Hazard lights also flash super fast. And sometimes they just fall off and stop blinking all together.


I've seen online if you replace the hazard switch it fixes this. In my experience, this does not.


There is another relay under the steering wheel, to the left a bit. You can find it by activating the hazards or turn signal, you'll hear it clicking. Pull it off it's connector, and your signal will stop. This is the culprit, the flasher relay.


Replacing this relay fixed my problem on my first W115 about 10 years ago. I've since gotten rid of that car and acquired another more recently, which developed the same problem.


I found a New-Old-Stock one on ebay, paid about $50 or $75 for it. I had taken my existing relay apart and attempted to replace some of the capacitors inside, and succeeded in making the relay stop working. I had also taken some three-prong flasher relays from an autoparts store and attempted to make one of those work, and failed as well, blowing lots of fuses. I'm sure it can be done but I couldn't make it work.


So, with this new relay from ebay it worked, but still was fast.


Most recently I discovered a flasher relay from a 1984 w126 300 SD plugs right in to my w115, with one problem. The blinker now works perfect, but my hazards no longer work. I'm satisfied for now, but welcome input on this subject. Thanks!

Depends on what model year /eight you are talking about. Pre-73 M.Y. /eights are different than the later ones.

From late '73 on the flasher unit is a standard (but with "bayonet" prongs) flasher unit. I replace them with a 552/536 unit by adding a short bit of wire and crimp on terminal ends.

https://www.amazon.com/CEC-Industries-TF552-536-Terminal/dp/B001DKJTVW

You can be pro-active and replace them with a LED compatible flasher also.

https://www.amazon.com/dp/B06XS8VX2W/ref=psdc_15729651_t3_B001DKJTVW

The earlier models have an integrated signal/hazard relay which can be converted but they require a bit more wiring change.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

The flashers you listed are two-prong, the relay I pulled out (original) has three, and the unit from the 300SD I installed actually has four, but still plugs in b/c the receptacle has four holes, plus an alignment. The new one from the parts car says "for use with a trailer".

If the flashers work with just two prongs, how do I know which one is which? Thanks

Do a "search this forum" in the vintage section for "flasher unit". My W114 coupe isn't available or I'd check for you.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now