This is a simple Fog Lamp Switch Circuit Diagram. This circuit recommended to have a rear fog light on a trailer with the additional
requirement that, when the trailer is coupled to the car, the rear fog
light of the towing car has to be off. The circuit shown here is
eminently suitable for this application. The circuit is placed near the
rear fog light of the car. The 12-V connection to the lamp has to be
interrupted and is instead connected to relay contacts 30 and 87A (K1,
K3). When the rear fog light is turned on it will continue to operate
normally.
Fog Lamp Switch Circuit Diagram
If a trailer with fog light is now connected to the trailer connector
(7- or 13-way, K2), a current will flow through L1. L1 is a coil with
about 8 turns, wound around reed contact S1. S1 will close because of
the current through L1, which in turn energizes relay Re1 and the rear
fog light of the car is switched off. The fog light of the trailer is
on, obviously. The size of L1 depends on reed contact S1. The fog lamp
is 21 W, so at 12 V there is a current of 1.75 A. L1 is sized for a
current between 1.0 and 1.5 A, so that it is certain that the contact
closes. The wire size has to be about 0.8 mm. The relay Re1 is an
automotive relay that is capable of switching the lamp current. The
voltage drop across L1 is negligible.
Author : J. Geene Copyright :Elektor Electronics 2008
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