Fitting 'Aux-in' connector to a Stereo Radio

[Old Sparky]

This is the circuit, incorporating the components suggested by Mark Hennessey, which i use when building 'aux-in' adapters for use with vintage car radios & stereos.  The values of R3 & R4, in particular, may need changing.  In one version I fitted a couple of 10k pre-set pots., adjusting them as required.  IF desired, the 'radio/aux' switch could be omitted and a switched 3.5mm jack socket used instead.  Alternatively, if grounding the 'unwanted' inputs isn't required, a double pole switch could be used instead of the 4 pole one.
(P.S. Apologies for my poor handwriting!!)