Help needed. flashing heater control lights etc.

[Lord Bungle]

Any ideas, W202 C220.
Tonight I got in the car and it started fine, but the lighting for the heater controls started to flash, a buzzing sound that seems to come from the interior lights and the illumination on the dash board / clocks alternates from dim to full while driving.
The flashing heater illumination stopped as soon as I put headlights on, as did the buzzing from interior lights, but the instrument panel carried on with the led displays going dim and full brightness.

I read a report on another forum that it could be the 'Heater black box' if this is the unit with solenoids under the bonnet I have replaced this with one from a breakers as when I acquired the car I was informed it didn't work.

The car ran fine, and repeat started several times over, so don't think its a low battery.

Any clue to what it could be? or do I have to go and make friends with my friendly independent Mercedes expert?

 

[whizzy]

It would be a good idea to have it plugged in to see if any codes come up

 

[LostKiwi]

That sounds like a bad earth.
In almost every case where different unrelated circuits interact in weird ways its an earth problem.

Unlikely a code reader will see anything on a car that age.

 

[Lord Bungle]

That sounds like a bad earth.
In almost every case where different unrelated circuits interact in weird ways its an earth problem.

Unlikely a code reader will see anything on a car that age.

I am suspecting the same thing.
Tonight I went out in it, no problem with lights at all.

 

[Uncle Benz]

Sounds to me like it coukd be a problem with the voltage regilator. It's built into the alternator. Particularly as increasing the electrical load reduced the effect. I'd test the alternator output first.