Can someone tell me where to find the speedo sensor on the back of the speedometer cluster?

My cruise control worked fine until I replaced my gauge cluster and now it doesn't work. I know the Amps are the most likely cause of cruise control failure, but I want to make sure it not the speed sensor first.

Thanks!

What model/year are we talking about?

I thought the speedo sensor was the same for all models. Am I incorrect? That might be my problem.

My car is a 1983 240D. The speedo I replaced it with was from a 1979 ~ 80ish 300D I believe.

On the 240D the speedo "sensor" is built into the speedo. There is an electrical cable that plugs into the back of the speedo unit. As I recall, there is a small black plastic piece that screws to the back of the speedo that accepts the cable. Last time I replaced my speedo, that piece had to be transfered from the old speedo to the new one. Do you remember connecting the cable to your new unit?

I do remember plugging it in.

It is black and directly behind the speedometer gauge - it is a 2 prong plug - correct?

That sounds right, but it's been a while. You may want to make sure it didn't come loose when you replaced the cluster, you should be able to feel it from below. If it still doesn't work, do you still have the old speedo to test with?