The turn signals on my 77 450SL just quit working. They started to click really fast, and I checked all the bulbs to see if this was the problem with no luck. Is this the turn signal flasher, or do I have a more serious problem???Please help!

Check the fuses.
I don't know if this applies to an older model like yours, but perhaps it could be the blinker relay?

As long as the turn signals still blink, it is not a flasher switch problem. Normally when the turn signal starts to blink fast, there is a broken bulb (but you haven't). I think the problem is to be found in the relay...

greetingz,

I had the same problem with my '72 280E. It went fast blinking all of a sudden but there was no bulb broken. It took a few months before it stopped blinking. This was indeed the relay as Mbenz said. In the relay there is a bi-metal and this bi-metal is just "tired" and stops moving. You have to change the complete relay.
I am not sure where it is on the 450 but on the 280 it was a piece of cake to replace.

My 450sl starts also doing funny with the turn signal. It goes from a little faster to normal and back again, wonder how long it will take till I have to replace it also.

Blinker Circus...
 

First, turn on your hazard flashers to see it the problem is just with the turn signals. Do they just blink fast on the right or the left, or is it either or both sides?

You don't have to have a "broken" bulb, it could just be a loose or dirty bulb or connection. See if you can isolate the problem. It may not be a relay.