Ottawa MG Club

Does anybody in OMGC have any ideas why the following is happening on my 1973 MGB?

Background:
Car has overdrive available on 3rd and 4th gears when the O/D switch is ON.
All lamp bulbs have been converted to LED with exception of alternator indicator and headlamps.
Overdrive being active involves 2 switches both being ON simultaneously. They are both in the Yellow wire circuit and permit the O/D solenoid to become active.
When this activation is stopped (O/D off and/or out of 3/4 gears) the solenoid deactivates.

Situation (unplanned self test):
When solenoid is STOPPED (but not when it is activated) there will be a simultaneous momentary flash of the indicator lamps for the hi-beam (blue) and left and right (green) signals. There is no effect on other dashboard lamps that are beyond the light switch and dimmer.

Supplementary comments:
This unintentional flash serves to confirm that the three bulbs are still working. Sort of like the brake failure indicator lamp test but on steroids. I really don’t need this!
LED bulbs, since they use so little power, are notorious for stealing power from the nearest source, including ground. This why dual filament LED bulbs can’t correctly run both filaments simultaneously which is a problem with indicators when lights are on at night. Modern cars do this by switching between filaments.

This isn’t hurting anything nor affecting the health or driveability of the car. It is just wrong.

Enjoy.

Michael.
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UPDATE from the LED manufacturer [ Classic Car LEDs ]
Hello Michael,
Thank you for your email.
An intriguing problem!
This is not something that has ever been reported in our ten year history and reviewing the wiring diagram, there appears no common wiring other than the fuse box itself and ignition switch. The issue that is manifesting itself could be caused by a small current surge when the switches are deactivated that is passing through the warning lights. LEDs will light with a lot less current than an incandescent lamp and also immediately switch on rather than warming up which an incandescent lamp does which is possibly why you are seeing this effect with the LEDs but not the originals?
To cure the symptom, a resistor to the value of the missing load compared with the incandescent lamps, in parallel with each warning light should stop the issue?
Kind regards
Duncan Rickards
www.classiccarleds.co.uk
Facebook - Classic Car LEDs
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AND AN UPDATE FROM MICHAEL COOKE:
This is the final piece of the puzzle. For the record. Could be an interesting topic in the proposed tech session. And there are 2 other related topics! Plus headlight updates.

Since the cause is the ‘surge’ current when killing O/D:
It can approach the LED either from the power side or the ground side. This will be hard to determine which, without doing one of these 2 fixes.
To fix it from the ground side add in a resistor. As described previously by the manufacturer. Kind of defeats the ‘efficiency' of LEDs but is brighter than incandescent.
To stop it approaching from the ground side, given that these LEDs are NOT polarity sensitive, the trick is to make it polarity sensitive by adding a plain diode to the ground side. On each bulb, possibly by first combining the three ground wires. No cost in efficiency. So do this test first.

Or ask the manufacturer to supply a ‘polarity sensitive’ LED. We’re still talking.

I can guarantee you will get similar problems from other manufacturers or Amazon. But with less or no assistance.

Cheers, Michael.