Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Roadster S1 Clock question

Sometimes a flash of voltage can interfere with polarity. Don't ask me to explain, but a way back a friend bought an MGB with the factory electric fan. It overheated, and it turned out that the fan was spinning the wrong way. It was a foolproof connection and connected right, and yet the fan was reversed. The dealer could not explain this. I think a replacement fan fixed it, can't remember now.

I would suspect the jump starting. Modern ECUs are very sensitive to voltage spikes, and why relays now have diode protection.

Very good!
Dave may have a point - I remember flashing a dynamo on my first Land Rover when converting from +ve to - ve earth.

Would have been useful at this point to have checked the actual polarity of the purple wire, to establish whether it is clock or feed fault?

Yep, purple wire and an earth using a voltage tester or a multi meter at 20 Volt setting will give you feed polarity. If that shows correct then flash the clock terminals to an independent battery or disconnect the battery terminals, or use a power pack to flash the clock. A further thought, has the clock got a diode fitted inside? might cause directional instability if it's failed.

Doc Brown says you've got to get it to 88mph https://en.wikipedia.org/wiki/Emmett_Brown

Easily done in a Roadster I believe but of course I can't condone that.

Only extra suggestion I have is checking the set button is not stuck somehow. Never heard of flashing a clock motor, this is only applicable to motors and generators with large iron cores that maintain residual magnetism. The purple wire to positive terminal on clock is factory correct.

There are several threads on Ford and Classic Mini clocks also running backwards. Common solution seems to be replacement. Shouldn't be too difficult to source one. Look for 52mm Smiths.

There are a couple of vintage Smiths car clocks here. https://brooklandsenginecraft.co.uk/Instruments/Watches%20&%20Clocks.html

Yes I have to agree with you there Richard, aren't they quartz anyway now? Large motors changing polarity or AC single phase to three phase on delta variants I have always carried out especially in the old days and when uprating the charging system on cars from positive earth to negative earth. Flashing clocks though does seem to be a well used reported method. Think I might go and have a rummage about in the parts bin and strip an old smiths clock and see what I can find or perhaps make it do!

Little more research, if you have the electro/mechanical later type it has two coils moving between the poles of a magnet. As the coils of the balance wheel move between the poles of the magnet a transistor was switched on providing a pulse to the coils to drive the balance assembly and thus the hands of the clock through a gear train. Perhaps it could be that the transistor has failed thus altering the switching polarity. Richard's knowledge needed here.

I checked the polarity of the purple wire with a test lamp. Wire to ground lights up the lamp so reverse polarity does not seem to be the problem. Will report back after further experimentation.

John