[Click on Photo]
Figure 1: Simple
|| When I first
acquired my 356B it had a 912 engine installed along with a mechanical tachometer. Seeing
how the mechanical tachometer will not work with the 912 engine, I quickly set out to
convert it to electric. After studying the electrical diagrams, I soon realized that the
tachometer line connects to the output from the points that drive the ignition coil.
Thinking about this in detail, I soon realized that the points that trigger the coil would
not work if the tachometer cable was accidentally grounded. With this in mind, it became
apparent that if I placed an electrical switch that swapped the electric tachometer cable
between the gauge and ground, I would have a handy ignition cutoff switch with very little
electrical ignition wiring diagram for early cars is shown in
1. As you can see from the diagram, placing an in-line switch that grounds the
tachometer signal will prevent the coil from firing. A thief may enter your car and be
able to hot-wire the starter, but he will not be able to get the car started because the
points will be grounded. The starter will turn over and over, but the car will not fire up
because there will be no spark for ignition. This basically has the same effect as
disconnecting the coil.
I chose to use a simple SPDT switch
from Radio Shack that allows me to alter the tachometer signal cable from the gauge to
ground. I placed this switch behind the dashboard so that it couldn't easily be seen from
the drivers seat, or from underneath the dash. The switch works really well, and will
prevent anyone from starting the car who does not know its there.
Comments, questions or feedback?
Feel free to drop us a line.
Here's an additional thought on the subject from one of
our readers, 914 owner Bill Kohnke:
Just a thought for the safety of
the car and a little theft prevention. I am a Ford salesman and through the years
have to explain to many customers about fuel shut off switches that are installed in all
Fords. They work in an accident situation by popping up mechanically from the force of the
impact and interrupting the fuel pump circuit. Just push the switch down to reset.
I have one mounted to the
firewall because if I ever oops & tag the ditch, tree, etc. I dont want the
electric fuel pump to empty the tank into an already bad situation.
For theft prevention a little
direct tap from a screwdriver handle and the carbs/FI will cease to run very soon or until
the switch is reset. This is great because who would be looking for a 1988 - 1998 Ford
part stashed above the relay box and cant be seen. The 19 year old has no idea why
the car cant run long enough to leave the cellar either.