In
the mid 1970s through the early 1980s, Guild offered an optional phase
switch. Phase switches were more commonly found (as standard) on some
solid body models, such as the S-100 and M-75, but they are quite
uncommon on archtops. The option is listed in the 1978 catalog thusly:
"A phase switch for reversing pick-up polarity is available on all
double pickup electric guitars." Shown below are a 1976 CE-100D (left)
and a 1978 Starfire VI (right) fitted with the optional phase
switch. Note the location of the switch is below the pickguard.