lights dim with extra load

[jabstick420]

not sure if this has been asked before, but I've noticed that when driving at night if I engage window switches or turn the AC on, the console lights and headlights will dim a bit.


more noticeable when I roll the window up, and the lights will dim for a second and then go back to normal once I let go of the switch.


normal?

[Diseasel300]

Normal, especially if you're idling. At idle the output from the alternator is pretty low, especially if you still have the original 60/70A alternator. With the lights on, blower motor running, and then engaging the switch for the windows, you pretty well exceed what it can put out. The dimming shouldn't be a drastic dim, but will be noticeable. If you're getting a big dimming, probably time for a new voltage regulator. Check your idle speed as well, if it's low, it will exacerbate the problem due to even lower output from the alternator.

[jabstick420]

whats the correct idle for 617 turbo?

[Diseasel300]

Not sure what the book says, but I'd expect it to be 625-650 RPM with the transmission in gear. In park or neutral, it will probably be slightly higher.

[jbach36]

I've never noticed it on my W124 300d, but for the longest time I didn't know that you can brighten or dim the dash lights with the (?) tripometer or clock turn knob. So brighten them up and see if that helps. Could also be that your bulb is dying and time to replace it.