This weird story is described in ‘The Secret Country’ by J and C Bord.
One evening in September 1974, Michael Byatt (a registered gliding instructor and senior NCO in the Air Training Corps) was driving his car up over Eggardon. Suddenly the engine began to lose power, and the headlights dimmed. He and his passenger became intensely cold and ‘felt an eerie presence’. In the sky they saw a yellow-blue [sic] light ‘in the form of an eclipse’ [sic – an elipse?]. It moved slowly backwards and forwards and ‘had a sort of glow about it’.
A couple of years earlier three cars climbing the hill at night had simultaneously stopped suddenly; they had no power and no lights, but these returned after a short time. Ooh sounds like your typical UFO incident.. or dodgy alternators.