Specifications

21
Words of caution
–
ALWAYS CARRY OUT A CURRENT DRAW TEST ON A
NY
CIRCUIT BEING IMMOBILISED TO ENSURE IT IS WITHIN THE CAPABILITIES OF
THE SECURITY SYSTEM.
A two or three point immobiliser has an awesome responsibility to perform.
Therefore, it is imperative that where the alarm interfaces with electrical circuits in
the vehicle for the immobiliser function, your joints must be perfect. Whilst the
failure of a starter circuit may cause a little inconvenience to the customer, the
failure of the ignition or fuel delivery system may have catastrophic
consequences.
* Ligh
t flash wires
-
If the security system manufacturer specifically states that the
alarm must be connected to the park lights, do not try to connect to the indicators
(which may invalidate the product warranty) as the current draw may burn out the
systems li
ght flash relay. This in turn may burn out light bulbs, and/or flatten the
vehicle battery. A lot more current is drawn flashing indicators than flashing park
lights.
Park light and indicator wires are commonly found at the steering column harness or
the
control relay. They are usually positive switching but can sometimes be
negative. Watch out also for some cars, usually European, that have separate left
and right side park lights.
* Door pin switch wire
-
Most vehicles use a negative switching system fo
r dome
light control, although there are some vehicles that use positive switching, e.g. early
model Ford Falcons. This wire can commonly be located in the kick panel area, or
windscreen “A” pillar, or under the dash at the instrument panel if the vehicle
has a
door display or door open warning light, e.g. Honda Accord or Subaru Legacy.
When testing for a door trigger wire make sure that the wire you have found works
when each door is opened, not just the driver’s door. A negative switching type will
show
12 volts when the door is closed and 0 volts when the door is opened.
Conversely, if it is a positive switching system, the wire will show 0 volts when the
door is closed and 12 volts when the door is opened.
12 volts
Door Switch
Dome Light
NEGATIVE DOOR TRIGGER
12 volts
Door Switch
POSITIVE DOOR TRIGGER
Dome Light
Be aware of vehicles that have one wire fo
r the front doors and another for the rear
doors. Connect the alarm wire to both of these wires using diodes to isolate the two
circuits. Some vehicles have separate wires for each door, e.g. BMW 5 Series.
Also make sure that the wire does not have a perm
anent ground on it when the
dome light control switch at the light is switched to the full off position, as this may