Hi list,
Here is a way to make a cheap polarity checking aid. Obtain a piezo buzzer (RS 273-059) and a diode (RS 276-1104).  Attach wire leads to the buzzer, Clip one lead to the negative terminal of a 9 volt battery (the larger one), test the buzzer by momentarily touching other buzzer lead to positive terminal of battery (smaller one), now put diode in circuit by attaching one of the buzzer leads to it . If buzzer sounds when other diode lead is touched to positive, diode is installed correctly, if it doesn't flip diode around.  Once device works solder or twist leads tightly and insulate them. This device will probably provide a buzz when it finds a 6 to 18 volt positive point.   


Lynn Roberts
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