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

Suggest having a word with Speedy Cables: they are the people responsible for the "Smiths" instruments used by Morgan - and very helpful in my experience.

Just sent them an email. Thanks for the suggestion.

John

Don't wish to be critical, but just for sake of correctness: A test lamp between two terminals will always light regardless of polarity.
As Sewin suggested earlier, the only sure way is to use a multimeter or DC moving coil voltmeter, which will show a negative reading or the case of analoque instrument, the pointer will go in reverse.

Just my thoughts but, unless the battery was in the wrong way round so the whole car was reversed then lamping from a wire to the ground will show a +ve on the wire on lighting?

K

Yes indeed, agree as long as it’s a true ground i.e. visible chassis connection, and not just using the other wire assuming that’s the grounded one.

Agreed ... just a bulb between the two wires would tell you nothing in terms of polarity as you say ... would have to be chassis ground

K

Point of clarification. I put the probe from the test lamp on the purple wire and with the clip on the other end of the test lamp I touched the under dash steel hoop. The light lit up, indicating the purple wire had power (positive). I then ran the probe from the black ground wire and touched the clip to the hoop and the light did not light up, indicating that the black wire is the ground (negative). If the purple wire did not light up and the black wire did light up, that would indicate that the battery was connected backwards. Of course, the two wires could be connected to the wrong poles on the clock. I didn't want to switch them for fear of burning out the clock.

John

John, others may have already advised you about this. Working under the dash with the battery connected is frankly asking for trouble. I've had my share of serious issues with car electrics over the past 50 years, including at least one (fibreglass) one catching fire. PLEASE get a professional car electrician to sort this for you.

I pulled the clock out of the dash and it had a manufacturer's name and part number on it. I contacted the manufacturer, Caerbont Automotive, and ordered a new clock this morning. Now I can experiment on the old clock to see if I can make it turn around. Will report results, if any.

John

Caerbont is the company that manufactures classic Smiths branded gauges.