After several of years of no cruise control on my '78 450SL I decided to fix it. Checked all the various components (there are posts & videos on how to check everything) and found all components worked. The cruise control amplifier seemed to be bad, a common problem.

I bought a Programma rebuilt unit and it did not work. I bought 2 used ones on ebay and they didn't work.

So I watched this YouTube video of how this guy repaired his similar amplifier on his W123. The W123 amplifier is a bit different from the 450SL unit but follow everything he did.

The difference with the older 450SL unit is there are only 2 capacitors and they are 47uf16 which I bought 15 for $8 on Amazon . Also bought on Amazon a $33 electronics soldering kit which worked great. "Solder Wick" is helpful to remove the solder from the holes where the 2 capacitors go through so they can be removed and replaced. Make sure you connect positive and negative correctly!! On the back of the amplifier board where the capacitor wires go through there is a tiny "+" so that you get it right. The long wire of the new capacitor is positive, the short wire is negative.

It took 20 minutes to replace the 2 capacitors and about 2 hours to re-solder every point on the back of the amplifier board. This was super easy and my cruise control now works great. I have never done any electronic work before and this was one of the easiest jobs I've done on the 450SL.

Brent Owens Aug/2025 FB