Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing +4 Buzzing (relay?)

I am experiencing an intermittent problem with the brake lights/turn signals on my 57 Plus Four. When applying the brake I hear a buzzing sound even though the brake lights are illuminated. The right turn signal works correctly, but not the left. Before dismantling the entire electrical system, and replacing perfectly serviceable parts, I wonder if someone might be able to provide me with some troubleshooting guidance. It becomes wearying to use hand-signals when making left turns!
Thanks
Richard

If you have dynamo charging, check its voltage regulator, These can make a suprisingly loud noise when playing up, sounded like a cooling fan on my Land Rover.

Indicators may be a separate issue. Make a start by checking bulbs and holders.

A couple of things to check on the buzzing from the brakes

1 Does it happen when you apply the brakes very progressively , so softly that you don't activate stop lights. Does the buzzing also stop?
If so I would check the hydraulic stop light switch itself, there was a vey bad batch of these a few years ago that got rough quality control and were hopeless, failing very quickly indeed.

2 Check the earths of all the rear lights , normally this is one bolt onto the chassis at the rear somewhere, but previous owners may have moved it almost anywhere, or installed multiple earths.

As Richard suggests I suspect the indicators are a separate issue which is not connected to the brakes, except that both are probably electrical. If the bulbs are all good, I would check that you have really earths (grounds) for all of the indicators. Secondly the indicator switch itself may have gone past its sell-buy date, and need replacement.

Gentlemen,
Thanks for the notes, I am still living with the problem. The buzzing is coming from the Lucas DB10 brake-and/or-signal relay-box when I apply the brake. The brake lights work despite the buzzing and the right turn signal flashes when selected (even with the brake pedal pressed). The left turn signal does not work at all, even without the brake pedal pressed. Is it likely that the failure is in the turn signal flasher unit? The type of flasher installed is not readily available at motor factors over here (one bolt to secure it, three screw type terminals), otherwise I would simply put in a new one and see if it cured the snag. Is there a simple test to check the serviceability of such a flasher unit?

I think the old three terminal flasher unit feeds both left and right via the indicator switch .... so if one is working the problem is possibly the switch ..... can you get to the wiring of the switch and bridge the terminals for feed and left indicator .... if they work the switch probably has an internal fault .

K

Thanks for the guidance regarding the flasher unit, it does have three terminals. I will remove the switch from the dash and bridge those terminals and see what transpires. If that is the answer to the "no-left-turn-signal" snag, then I imagine that the DB10 box buzzing when the brake is applied must be an unrelated issue. Maybe a coincidence that the two discrepancies seemed to occur simultaneously--sort of each being the others red herring.

This is a typical indicator flasher wiring diagram of the period. Yours will be similar including generic cable colour codes, excepting the warning light.



As you can see the flasher unit is before the indicator selector switch so if it flashes ok on one side it should be ok. If your check of bulbs, grounds and other connections is fruitless the next suspect is the selector switch. Shorting the flasher cable (shown green/brown) to the green/red (left hand) indicator feed will bypass the switch to prove if faulty or not.

Thanks very much for the helpful info, especially the wiring diagram for the flashers. It would seem that there is something out of order in the switch (which was new when the restoration was completed in Sept 2019), so I will take a closer look at the security of the wires contained within. The other snag, that with the buzzing from the DB10 relay box, still has to be addressed. It sounds as if the coils are trembling, causing the irritating buzz. I have cleaned the relays points, but the noise continues, but doesn't seem to affect the brake lights or the function of the turn signal (currently right side only). Is there an adjustment that can be made to the relay points gap?

Just checked and the Lucas DB10 box allows brake lights to be used as rear indicators, so that explains the connection with the buzzing relays. You could try cleaning the relay contacts with abrasive paper again, and making sure no high resistance connections to box. Here is wiring diagram.



Would he interested to know if this was ever a factory fit as I imagine it would be illegal in the UK. Here indicators are required to flash amber.

This is the internal layout of the brake/indicator relay .... the mystifying thing is that if you are not indicating there's no power to either of the coils (and no pathway from the brake circuit to the coils ) .... just the earth at one end ... you mention you cleaned the contacts in the DB10 ..... can you operate the indicators with the cover open and see if the relay operates if the contacts are closed because they are stuck (or because of lack of switching signal from the indicator switch .... there may be some unplanned pathway for power to get to the coil from the brake side. One thing to try if the left indicator doesn't move the contacts is to try gently opening the contacts with something insulated while someone presses the brake and see if the buzzing stops.

Richard .... in the US (for sure) and I guess Canada ... having your brake lights double up as indicators is common .... especially on older cars

K


Ps I think Richard's suggestion of cleaning all earths and contacts should be your first port of call .... always good advice if mysterious things are happening with your lights