Radio Buzzes w/lights turned on

[William]

Turning on the lights.........rotating the light switch on the dash in a clockwise direction to either the Park or Head lights position, it doesn't matter, causes a buzzing noise in the radio. The buzzing noise is the same whether the engine is running or not.

Also, when rotating the light switch on the dash in a clockwise direction to either the Park or Head lights position, the "bulb out" light on the dash will come "on". The thing is, there is never a bulb that is actually "out".

If the solution is to replace the "light switch" on the dash, how would I go about doing that??

[hill]

Model? Year? Do's it have a good ground connection from the headlights?

[William]

This is a 1986, 420SEL. Please tell me how/where to check the ground on the head lights. I do know that the car's grounding strap has just been cleaned and reconnected. Thank you for any further comments.

suggest you check the shielding on your radio antenna wire. A bad connection on the shielding cover will allow spurious noise pickup from electrical in car. Check wherever there are connections looking for corrosion. If everything is good check out Radio shack for interference filters that go on your radio B+ line to filter out electrical interference. How is the reception on the radio for distant stations? If not good - suspect antenna connections for sure.

[Zeus]

Sounds like you might have a ground loop. Try playing a cassette with the lights on and see if you still get the buzzing noise. If you do, you have a bad ground connection somewhere. If your stereo is quiet with a cassette playing and the lights on, I'd check the antenna as in the previous post.

Also, have their been any aftermarket mods done to the stereo? Any amps, speakers, etc. added?

[William]

Many thanks for the good suggestions. In response to the last one, there have been no modifications.

The engine was recently torn down and rebuilt and based on the opinions that I may have a "grounding problem" I'm hot on the trail. I would never have guessed it, so I'm very grateful to those who took the time to respond.

[MikeTangas]

Now are you sure you don't have a bulb out too? Turning the switch CCW activates the 3W parking lights either left or right (one click or two). Your front blinkers should be dual filament bulbs, might be only one filament is burnt (the 3W side) and when you hit the parking light the bulb out indicator comes on accordingly.

Since the engine was recently out, check to be sure the grounding strap was reinstalled between the engine and chassis.

[mreid]

Sounds like a bad ground. I have seen bad grounds do the strangest things. Drive a guy to drink and drink and......

[SCLJA]

The radio in your car should be a becker 754 and it more than likely has some bad internal filter capacitors. The other thing I would check is your antenna ground at the power antenna if the noise is only on radio and not tape. Good luck!

Scott@Lajollaaudio