Fitting a "lights on" alarm to a V8
Alan Turner (Damask 0663) from Devon posted a note on the V8BB and
in passing mentioned a useful modification. Here he sets out how to
make the device. (Mar 05)
Alan recently acquired his V8 and comments
"Isn't it strange, when returning to a classic for everyday transport,
that you miss those little "insignificant" things like central
locking, electric windows and headlamp warning alarm". Not
wishing to get stuck with flat batteries by leaving my lights on,
I decided to find an alarm for the side/head lamps. A search though
Maplin's catalogue revealed a kit available for £7.99 plus postage.
I found it was out of stock but put on a back order and eventually
The kit is K3505 Car Headlamp Indicator order code VF24B and
is on page 495 of the latest Maplin Autumn/Winter 2004/2005 catalogue.
The kit comprises of a small printed circuit board of good quality
with two mounting holes for M3 studs, 10 diodes, 10 resistors, 7 capacitors,
2 integrated circuits with sockets, a transistor and a buzzer. Most
of the components come on a tape, which are in fitting sequence, there
is also a booklet with information of board layout, circuit diagram
and resistor colour codes.
kit was the easy bit as far as I am concerned, but I am an electronics
test engineer. It took a couple of hours to complete.
its board alongside a 10p coin to illustrate the small size
of this unit. (Photo: Alan Turner)
The connections to the outside world are ground, ignition and
sidelights. I fitted a jumper across J2 to prevent a warning when
ignition is switched on without lamps on (required in some countries).
So the kit has two possible configurations. The kit was wired up
for test and worked first time.
plastic box was found and the board mounted inside to protect
it from damage. I marked and drilled
the holes for mounting
before fitting the components to the printed circuit board populating
the board, Two M3 countersunk screws with nuts fitted to space the
board off the box. Remember to drill a hole in the box line with the
buzzer or it will be very quiet.
Now to find somewhere to fit the box, secure it and get the required
feeds to it. Well there is a square section tube running under the
dash which had already been used to mount the fan override switch
and the box would fit nicely with a couple of cable ties around this
tube section. A feed was taken from the ignition, a white cable near
a bullet connector under the steering column, the light switch was
carefully prised from fascia and the sidelight feed cable is red with
a green tracer. Piggy back connectors were used for both of these
feeds and a eyelet crimped to the ground cable and a suitable position
found. Job done.
The alarm sounds when the ignition is switched off when the lamps
are still on for a few seconds and then repeats a couple of times
and is then silent, so sidelights could be left on if desired.
A few notes worth
o A multimeter (DVM) is useful to trace feeds, but a test lamp could
o Static precautions should be taken when handling semiconductor
electronic components.o If using cable ties, do cut the surplus
off really flush or a very sharp edge can result, which can cause
cuts especially when working in a confined spaced. There is a special
tool available for this task
Tools required are a soldering iron (25 watt), side cutters, long
nose/ round nose pliers, and a small flat blade screwdriver. You
will also need solder and connecting wire/connectors.
Integrated circuit is an electrical component consisting
of many semi conductor devices encapsulated in one package, usually
having a minimum of eight legs.
Static precautions usually take the form of a wrist strap
which is connected to an earth point (on a 13 amp mains plug) with
a 1 ohm resistor in the line. The concern with static is the person
handling the components can obtain a high level of charge which
could be discharged through touching an earthed unit. The earth
strap and resistor lets this discharge. We are all familiar with
the small shock when touching a door handle in dry weather, well
this is the static charge on you discharging to the handle and not
the handle being charged. So if you were to charged with static
you could discharge through a semi conductor device, integrated
circuit or transistor and the device could be damaged or its life
reduced. In practice you often get away with it.
Small plastic box - you can get these from Maplin or Farnell.