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

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.