this issue used to be very intermittent, it is starting to increase in occurrences now. The interior lights will flicker (climate control, dash lights, etc), the radio will lose the bass (it actually cut completely off momentarily today) steering wheel control lights will come on and off, passenger airbag light will flash on and off. Then if you restart the car 9 times out of 10 everything will operate normally. What are your thoughts? Voltage regulator going out? Alternator itself going bad? Car starts without issue every time, so that tells me that the battery should be good still. Car is a 2004 CLK500.

 

with a multi meter across the battery terminals with car running, voltage jump from 13.9-14.9 and everywhere in between.

 

I have the same year and model of W209 as yourself and last month I had electrical issues as well. You didn't list your mileage but if it's past 60K miles, I would consider the Voltage Regulator as a possibility ($65 part BTW).

I had the same issues as you did, the problem turned out to be the battery. Take a look at the thread below, I listed my debugging timeline and I posted some useful PDF files just in case it's not the battery.

https://mbworld.org/forums/clk-class...t-battery.html

Good Luck and please let the W209 community know what the problem ended up being.

 

ok, it ended up being my voltage regulator. $57 at the local dealer. Took me a while to replace since I could not get the alternator out of the car, had to just twist and turn it to get to all the screws/bolts to replace it. Voltage is stable at 14.4 now.