740 - Buzzing Behind Dashboard & Lights Warning Light

[islipaway]

Hey, this seems unrelated to my major idle issues in the other thread so I thought I would ask here, hope that's okay.

Recently I've had an intermittent buzzing from behind the dashboard, sounds like it's coming from the top right corner while driving, sort of where the coil is in the engine bay. Any ideas what this could be? Doesn't seem to be effecting anything at the moment other than my sanity. Sounds like a rasping sort of noise.

Another tax on the old noggin is the dashboard warning light for a blown bulb is on but I can't find any blown bulbs. Does this light go for interior bulbs too, are there any weird hidden ones I might not have noticed? Should the center brake light on also be a running light on the rear door of an estate?

[Laird Scooby]

Could just be an old bulb or two in the car or have you recently replaced some bulbs?

[islipaway]

Nope, seems to come on/off sometimes when I press the brake (as in pressing the brake sometimes makes the warning light go off!) I noticed today so probably rear running light or but they all seem to be on from visual inspection, will check earths etc. Just checking if internal bulbs would cause the dash 'light out' bulb to come on mostly. The buzzing is more concerning but it didn't do it today *shrugs* put it down to gremlins!

[Laird Scooby]

That sounds like a bad earth connection on the light clusters and possibly a bulb in the wrong way round.
The stop/tail bulbs have 2 pins on the side to hold them in the bayonet fitting, one pin is higher than the other so it should only be possible to fit them in the correct way.

Somehow people still manage to fit them the wrong way round which means they have to push really hard to get them in the socket before turning them to lock them in position.

The fact the bulb failure warning light goes off when you press the brake and bring the brake lights into the circuit as well as the tail lights suggests this is probably the case.

This pic shows what i mean :



When it's just the running lights on and one bulb is in the wrong way round, the bulb failure will see a brake light and a tail light instead of two tail lights. When you press the brake, then it will see two brake lights and two tail lights which means it will be balanced.

For the purpose of that explanation i've ignored the high level stop light which is on the left hand brake circuit but the basic principle holds true so check the stop/tail bulbs are fitted correctly.

Also the interior lights aren't monitored by the bulb failure, just the obligatory external lights.

[OldBlueVolvo]

One thing that can cause a buzzing sound is a relay switching very rapidly. They shouldn't do that unless there's a problem in the circuit.