A pair of improved jumper cables one end of which automatically lights when the other is arbitrarily connected to a source battery and also automatically indicates the polarity of the source battery by means of light emitting diodes. Also when a pair of probes at the lighted end is arbitrarily connected to the destination battery, the polarity of the destination battery is automatically indicated by means of light emitting diodes. The polarities of the source battery and the destination battery are displayed together on the face of one of the clamps at the lighted end. By a comparison of the indicated polarities the correct connection can be made.