This unit is to be found on 100 models only that were manufactured before mid-1985; owners should note however, that the
switches may well have been removed from, or blanked off on, models built before that date
The switch is a small unit retained by two screws to the right-hand side of the throttle body mounting bracket; a vacuum
line joins it to number 1 cylinder vacuum take-off point.
The switch's function was to improve economy and part-load running by bringing a second pre-programmed advance curve
into operation. However this was found to have so little effect that it was omitted from all later models.
If a fault arises which necessitates inspection of the switch, disconnect it and remove it from the throttle body.
Insulate its connection and tape the wire back to the loom, then remove the vacuum line and fit a small cap, as on the middle two cylinders,
to the vacuum take off point.