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

The diagram above is useful in showing how the DB10 relays provide the desired effect. The asterisked text however appears to give instructions on removing the shared rear lamp function and possibly adding a hazard function, although Image has not posted the associated wiring diagram.

If restoration to the more conventional separate brake and indicator lamps were required, I would suggest removing the DB10 unit altogether for simplicities sake.

ETA: Having seen the internal schematic of the DB10 it offers the possibility of a faulty relay failing one of the indicator circuits since their coils replace the indicator bulb load then repeat the flashing. Another reason to bin the unit.

Richard W ..... the brake/indicator thing is 'conventional' on the other side of the pond

If Richard S was keen to keep the lighting original then there would be the possibility of a couple of ganged modern cheap relays to do the same job (maybe even fitting into the original case) rather than the £80+ for a replacement DB10

Richard S ..... do you have a multimeter? ..... it would be interesting to know if any voltage was appearing on terminals 8 or 4 when the brake was pressed.


K

Ps Richard w .... not sure the coils replace the indicator load .... think they just connect the relevant bulb load to the flasher depending on which one is energised?

Pps ..... the image came from the MG Magnette page and was part of an article about fitting hazards to a DB10 equipped car and I thought the whole thing might muddy the waters

Thanks for update. I now understand the need to keep dual use lamps although the means of such adds complexity and as has been proven unreliability.

Thanks for confirming the source of article as well. Although it wasn't relevant it did provide a useful schematic. This shows one or other relay coil triggers the matching indicator circuit simultaneously isolating the brake circuit. Apologies for suggesting otherwise

If the left hand coil is faulty it could cause both the vibration as coil tries to trigger contacts and therefore fails to connect that sides indicator circuit, momentarily dropping out with the extra load. This would explain both the issues the OP has. It could still be a high resistance connection on the left hand indicator connection to DB10, pin 4 however. Best to check all connections to it particularly its earth.

I wouldn't recommend adding any further complexity building similar device. Bottom line to the OP, confirm the DB10 is faulty and if so then buy another.

Okay ... we'll agree to disagree on this ..... from your posted wiring diagram that includes the DB10, the indicator switch just puts a fixed 12v onto the relevant coil (via terminals 4 or 8).... the coil pulls in the contacts putting the indicator lamp load (2&3 or 6&7) onto the flasher relay (via terminal 1).... simultaneously isolating the energised side from the output of the brake light switch (terminal 5) .... the 12v on the coils stays steady until the indicator is cancelled.

Unless you're using a different wiring diagram from the one you posted ?

Either way, life's too short to argue over it so I'll leave it here.


K

Richard S ..... it's been bugging me how the brakes could make the relay buzz .... however although the 12v for the brakes comes in on terminal 5 it goes out on terminal 3 and 7 ..... Right next to the feeds to the coils ..... they're screw terminals I think so I'd check that there isn't a stray 'whisker' of wire bridging between 3 and 4 or 7 and 8 ........ if not look inside and see if there's any possible shorts on the way from those terminals ..... it may be metallic dust causing a high resistance short so a careful clean round that area with a brush may be an idea ..... the indicator problem could also be the switch or the coil on that side .... if you have a multimeter indicate left and check if there's 12v between terminal 4 and earth .... if not the switch and the associated wiring is a suspect .... if there is, cancel the indicator and look at the resistance between 4 and earth ... not a clue what it should be but it should be substantially the same as from 8 to earth ... if not it's likely to be the relay that's at fault.

K

Gentlemen,
Again, my thanks for your efforts in helping me try to solve this snag. I am going to be out of town for a few days, but will jump on trying your troubleshooting suggestions when i return.
Thanks v much
Richard
PS Richard W --we seem to have an appreciation for similar vehicles, I also own a Defender and a BSA 441 Victor Special.

Richard w .... our edits/posts passsed in the ether


Richard s ..... I would guess Morgan ownership is possibly indicative of a state of mind ..... Defender 90 (300tdi) Harley Knucklehead and '63 Triumph speed twin here

Enjoy your trip

K

I had heard the shared rear lamp coupled with DB10 was used on some early Series Land Rovers and may even have been legal in 60's UK. My thoughts are that the 21 watt bulbs aren't going to last too long being used by two intermittent triggers though.

A dual pin base might have worked if you could find suitable twin filament bulb. Nowadays a clear lens and dual colour LED would offer a solution.

I have delved further into the snag and have repaired the turn signal problem, which turned out to be the wire in the switch having somehow released itself from the screw-down terminal. A somewhat fiddly job getting the wire back into place and tightening the retaining screw. The buzzing continued and intensifies with firmer brake pedal application. I am going to borrow a DB10 that I know is serviceable and see if that is the cure. I have plenty of time now, as the car has been prepared for its winter sleep after we received a good measure of snow a few days ago. I will update you with the results of the DB10 swap when I have completed it. Just as an aside, the serviceable DB10 will be being provided by an MG TD owned one of my pals. The TD has the same brake/signal switching function as the Mog.

Hopefully the replacement DB10 will solve the issue and highlight the fault with yours. Might be worth changing the brake light switch as well given brake pressure changes the current buzzing, suggesting an intermittent switch. The contacts on these have limited life carrying intermittently up to 4 amps from the two 21 watt bulbs they feed. Its a cheap and easy replacement which I've done without need of bleeding brakes.

I have also changed the brake switch without bleeding. Dead easy if you have everything ready.