['LIVEWIRE?']

A recent (May 2015) post in the 'Vintage Audio' section of this forum has highlighted a problem which arises when attempting to recharge the internal batteries of a connected device via the cigarette lighter socket of a negative earth vehicle whilst the Ipod, etc., is plugged into the 'aux-in' connector fitted to radios in the Motorola 717/828/727/828/737/838 series, and their Radiomobile equivalents (900/920/970/980/1070/1080, etc.) In these sets the volume control 'cold' side, and hence the screen of the 'aux-in' cable is connected to AF positive regardless of the radio's (or vehicle's) polarity. Thus, in a Negative Earth) vehicle, a short circuit will exsist betwen the 'aux-in' lead's screen and the radio Positive Line whilst the IPod or other external device is plugged in, due to the fact that in probably all audio devices the signal return path is common with the negative line of the IPod. Ideally any adaptor should incorporate a 1:1 audio isolating transformer when used with the above range of radios, and possible a few other Radiomobile & Motorola models made between 1964 & 1974. AFAIK, later models, and all other makes of which I know have their Volume control common side connected to AF Negative, and the above fault will not arise.