Lighting System

[Concrete-crusher]

I am trying to sort out a few bad earth problems and realise my lighting wiring looks like a plate of spaghetti , can anybody give an overview of how the two relays work and what the markings on them mean.

I seem to have a lot of cloth covered wires here rather than those shown in the wiring diagram.

Thanks Steve

[billwill]

Relays are used so that the heavy current required by the headlights does not have to pass through the rather light-weight switch on the dashboard.

So the dash-board switch and column dipswitch control the current to the coils in the relays. Basically one relay for main beam and one for dipped beam. The heavy current (up to 9amps per bulb) pass through the output contacts of the relays, which are rated for 20 amps (I think).

The headlight flasher if still installed complicates the issue and I don't know off-hand how that is arranged.

[oldelanman]

The headlamp relays also ensure that the lamps are switched off when the pods are lowered which is why they are operated via a microswitch on one of the headlamp pods. Early cars had only a single relay located "upstream of the dipswitch which served only to switch the lights off when lowered and did nothing to reduce the current load through the dash and dip switches. On later cars (S3 onwards) the single relay was replaced by two - one for main beam and one for dipped - wired as Bill describes and having the added benefit of reducing the current load through the dash and dip switches.

The flasher relay is there to switch the main beam on (flashing) when the pods are raised with the dash switch in either OFF or SIDELAMP positions, it is operated by another microswitch on the other headlamp pod. In practice this feature is of little use and many have deleted it completely.

[lesesq]

Can anyone tell me where the relay and the microswitch are located or describe the appearance before I try to track them down on the old wiring diagram I have?

[oldelanman]

The "microswitches" are in fact courtesy light switches and are mounted on the rearmost part of the headlamp pod pointing upwards to contact the underside of the wing when the pod is closed. Headlamp switch on RH pod and flasher switch on LH pod. I have replaced mine with "proper" microswitches mounted on the stop bolts which you can probably just see in the photo.

The location of the relays themselves depends on the model I think - on S4 (and also S3 I believe) they are mounted on the inner LH wing below the bonnet hinge. I don't know where they are on earlier models but I'm sure someone will be along shortly to advise. They may have plated metal cases or black plastic ones as shown in the photo but will be the same basic shape.

S4 relay location