UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Vintage 70's 'Realistic' car radio wiring

julie_m · 3rd Aug 2018, 9:16 pm

You should be able to see what it is connected to using a multimeter. Select a low ohms (Ω) range, and measure between the mystery black wire and each of the power leads, with the set switched off and on in case the switch is in circuit, and with the probes both ways around in case there are any diodes in the path. Post all 8 results, together with the readings when the probes are not connected to anything at all (open circuit) and also with the probes touching each other (short circuit).

It most probably will be either another earth connection, or a supply to an electric self-extending and retracting aerial which is only connected when the radio is on. (Do all the above tests without a cassette in the slot, in case inserting a cassette cuts the aerial supply -- after all, there's no need for it to be deployed when listening to a cassette, and some people would be extra impressed by it retracting under such circumstances. Otherwise, what's the point of even having an electric aerial?)

In any case, the measurements won't lie .....

3rd Aug 2018, 9:16 pm	#7
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Vintage 70's 'Realistic' car radio wiring You should be able to see what it is connected to using a multimeter. Select a low ohms (Ω) range, and measure between the mystery black wire and each of the power leads, with the set switched off and on in case the switch is in circuit, and with the probes both ways around in case there are any diodes in the path. Post all 8 results, together with the readings when the probes are not connected to anything at all (open circuit) and also with the probes touching each other (short circuit). It most probably will be either another earth connection, or a supply to an electric self-extending and retracting aerial which is only connected when the radio is on. (Do all the above tests without a cassette in the slot, in case inserting a cassette cuts the aerial supply -- after all, there's no need for it to be deployed when listening to a cassette, and some people would be extra impressed by it retracting under such circumstances. Otherwise, what's the point of even having an electric aerial?) In any case, the measurements won't lie ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.