Dinsen > Matra Murena > Electrics > Driving lights

Driving lights

The Danish traffic rules require the use of driving lights at all times. This is the same in Sweden and Norway. This note discusses ways to implement that effectively.

Cars with popup headlights suffer from using daylight driving lights - imagine what it does to the aerodynamic drag of the car having to drive with the headlights up at all times!

When this rule was implemented, it actually reduced the number of accidents, so it is a good thing. And even if it was'nt I would be up for a fine if I didn't comply, so discussing the rule is really quite academic.

But it's not as bad as it sounds, because the rules allow use of dedicated daylight driving lights or fog lights for daytime use. On the Murena, the driving lights in the front bumper, can be used, but not directly as they are (per standard) only on with the high beam (light lever is turned twice, and lowered, and driving lights button is depressed).

Roy Gillard has concieved a very simple modification enables the use of the driving lights with the sidelights: The wire supplying the switch must be moved so instead of supplying the switch only when the high beam is on, it now supplys a voltage to the switch as soon as the sidelights are switched on.

However, since it is not legal to have the driving lights on at the same time as the low beam, a simple modification needs to be made on the fuse board so the driving lights turn off when the low beam comes on.

This is very simple, and requires no changes to the wiring on the car, that I think it is sufficient for most Murena's on the roads. After all, most are not used daily.

Fuse board with Roy's modification
Fuse board with Roy's modification automatically siwtching the driving lights off when the low beam comes on.

Automatic solution - add-on

This describes the driving lights implementation I originally concieved and described in this article. I now think the above is better.

The driving lights need to go off when the low beam is turned on - otherwise I'll get a fine as we aren't allowed to have the fog lights running with the headlights - unless there is a fog, of course. So an extra relay is needed: When the headlights are turned on, the fog light automatics is switched off. That will cost me one more relay.

There's one more thing, though, something that Lennart has talked about whenever I have discussed driving lights with him: It is not optimal to have the 2 x 55W lamps on when the engine is not running yet. It would be better if they didn't turn on until the charge light went off.

This requires one more relay. We are now at the count of three! Or we could use a transistor. The transistor is long lasting and will not load the charge light output of the generator, which is good as it is reported to be a bit unstable.

All this can actually be installed in the front of the car, e.g. in the fuse box somewhere. The charge light wire can be picked up from the wire harness in the front compartment.

Most cars here with driving light automatics cannot turn it off. This causes some blinking by other friendly drivers when you go south - they think you have forgotten to turn off the lights. They don't know that you have no option at all. I owned a Fiat Punto once - the headlights were turned on at all times with the stalk switch, since when the ignition was cut, the lamps turned off anyway. And it could easily be turned off by turning the stalk switch.

We might be able to implement something similar, but that would involve some cutting of wires which I'd like to avoid. Instead I want to have a dedicated way to turn off the driving lights. And since I do not cross the border to Germany on an every day basis, it would be ok for me if I needed to pull over, open the front bonnet and "do something" to turn it off.

Therefore I have included a switch to switch off the ignition signal to the driving lights automatics. This can even be a low power switch since it is only driving three relays.

Better driving lights diagram for Murena

A potential improvement would be to add a capacitor to leave the engine running unloaded a short time before actually turning on the driving lights. The value of the capacitor will have to be experimented with, but it should probably be in the range of 100 uF with a 10k resistor to charge it through. That would leave the light off for a couple of seconds. To design this is left as an exercise to the reader!

This completes the driving lights installation. Obviously the transistor and components will need to be soldered on a peice of wero-board and enclosed in a small box with wires properly fixed. It can probably be fitted inside the fuse box. Some might feel more comfortable using a relay instead of the transistor circuit, and that will probably work fine as long as you ensure that the additional load created by the relay coil will not hurt the generator.

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Page updated: 2007-11-01 08:53:18