It may matter whether your Morgan is LHD or RHD, since the gauges are switched. I have a 1961 +4 four-seat and a TR4, both are LHD. The LHD TR4 cable looks too short for the Morgan, but a RHD TR4 cable might be longer. Since the Morgan and TR4 tach gauges are interchangeable, a RHD TR4 cable should work on a LHD Morgan +4 if it is long enough.
Interchangable but there are subtle differences between the two guages!
Arwyn
