I have a 1960's gyroscopic turn indicator which I would like to power up. It has, what I presume to be, some kind of standard connector and the plate confirms 28 Volts DC.

The pins are labeled "A" and "B".

How would I confirm which way round the polarity is? Neither pin is connected to ground/the chassis.

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  • $\begingroup$ Because the pins are probably simply connected to DC electric motor, likely neither polarity won't destroy the gyro and incorrect connection will then result in opposite indication. But of course, I can not know for sure if there is any mechanical or electrical detail which would cause (immediate) damage when reverse-powered. $\endgroup$ – Martin Dec 24 '20 at 20:51
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    $\begingroup$ I have found some schematics of new indicators which list pin A as positive and B as negative..... $\endgroup$ – Dan Dec 24 '20 at 21:17
  • $\begingroup$ If I were you I'd open it up and see how it's wired. That usually answers the question, but Martin is right, the polarity will likely make no difference if it's a DC instrument, other than the wrong one giving you the opposite indication of what is desired. $\endgroup$ – Juan Jimenez Jan 1 at 20:16

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