11 Brookside Drive, Wilbraham, Massachusetts 01095
FOR COIL AND IGNITION
Switch must be ‘open’ (off position) for starting. Turn
‘on’ for oil fait protection. Should oil pressure fail, the
‘idiot light’ sending unit will ground out the ignition
current going to the points and spark will cease at once. Since
ign. is grounded out through the coil’s load, the wires will
not get hot and/or overload the circuit. Maximum current draw is
the same as when points are closed: about 2 amps.
FOR MAGNETO IGNITION
Here the safety feature functions like a remote control magneto
kill switch-which it is, since the oil light switch grounds out
when there is no pressure. To start the SPST switch is in the
‘open’ (off) position – so that the oil switch won’t
ground out the mag. After the startup, close the switch for
Ioss-of-oil-pressure protection.
You can save wire and time by using a single-contact style oil
sending switch such as used on Chrysler products. Slant six and
most V-8 engines. These switches are closed when
no pressure exists-thus supplying a ground for the bulb; they
open with pressure, eliminating the ground.
Simply wire the switch up with a single pole-single throw (SPST)
switch in the line as per the diagrams enclosed. It will work for
either coil and battery or mag. ignition. It simply grounds out the
coil or mag in the event of oil pressure loss.
I do wish to point out that most oil pressure light sending
switches open (break contact) at about 15 PSIG and close (make
contact) at about 7 PSIG. So if the engine in question runs at less
than 20 PSIG, then the system cannot work. Many older engines use a
pump-splash system to wit: Chevy 4 cylinder, Chevy 6 cylinder, 1930
to 1953, model A Ford, Dodge fours 1914-1928 etc. which never
exceed 15 PSIG under normal running (some Chev. engines will, but
don’t count on it).
Also, be sure your pressure sending switch is for a light – the
units used with gauges are of the variable resistance type and will
not work for this application.
A high temperature cut-off can be improvised by using a ‘hot
light’ single contact switch instead of the OK unit switch-or
in conjunction with it. These units are normally open and close at
about 250° F. If both switches are used, wire them in parallel;
then either low oil pressure or high engine temperature will kill
the ignition.