Changeover relay wiring

[gs.davies]

I'm about to fit some LED front indicator bulbs which also incorporate a daylight running light. It's occurred to me that these probably ought to switch off when I switch the either the sidelights or the headlights on.

Could I put the coil of a suitable changeover relay in parallel with the side/taillamp feed or does a relay coil have to be on a circuit that's not seeing another load?

I'd use pin 30 for the supply to the controlling relay, 87a to the DRL meaning that when the coil is energised, output would switch to 87 which would have no connection and thus extinguishing the DRL.

Pin 85 would be connected in parallel to the sidelight feed with 86 going to ground. I've established that the sidelights are always on with the headlamp switch in position two or three.

Does this make sense?

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[timmy201]

You could also just use a “normally closed” relay which turns off the power when it’s triggered

[Polarsilver]

not sure how you intend to power these daylight runners or how you will switch them on ..maybe ignition fed always On ?.. then could use the normal sidelight 12v supply to switch "using Timmys" additional NC Relay Coil to turn Off your daytime lights power supply when the standard sidelight lighting is required.
Garry are you sure this is a good idea .. why not just use the standard Headlights in the Daytime if it is a "Scary" Driving Day .

[Peter Laidler]

I'm thinking the same thing Norman. If it ain't broke and all that......

[gs.davies]

not sure how you intend to power these daylight runners or how you will switch them on ..maybe ignition fed always On ?.. then could use the normal sidelight 12v supply to switch "using Timmys" additional NC Relay Coil to turn Off your daytime lights power supply when the standard sidelight lighting is required.
Garry are you sure this is a good idea .. why not just use the standard Headlights in the Daytime if it is a "Scary" Driving Day .

It’s a relay which is in one position or the other, switched to its second position via the energised coil, which I hope can be achieved when the sidelights are on.

The actual bulbs are dual mode; one contact is amber for indicator the other bright white for the blind idiots who don’t look for cars, let alone tiny ones anymore between their phones or dashboard iPads. These lights are intended to be powered from the ignition on position of the key (essentially the green side of the fusebox..)

Honestly, last year I had enough of people not seeing me, I drive this quite a bit and whilst I’d rather not have to make these kinds of mods, it’s really because most other road going appliance drivers just don’t look for objects anymore, just lights.

Using standard headlamps all day is a drain on the battery too. I’m still on dynamo, and don’t currently have a plan to go to alternator with the very low demands of led lighting.

[timmy201]

Our Aussie cars have clear lenses and a dual filament base. The factory set them up:
Parking lights (side/running lights) are white
Indicators are also white
When you have the parking lights on and then use the indicator they flash white on white which is a bit confusing for modern traffic

The headlights only had dipped and main beams, no sidelight

I swapped mine to the LED switchback type:
Parking lights are white
Indicators are amber
When you have the parking lights on and then use the indicator they flash amber, and the white parkers automatically turn off and then back on when the indicator is turned off.

Unless you have some specific lighting regulations you could just leave your drl bulbs lit all the time?

[gs.davies]

Tim, if our cars weren’t on the opposite sides of the planets, they could be twins…

That’s exactly the set up I’ve gone for, a white lens and a switchback led. I don’t really give too much of a stuff for the lighting regs, as it seems to be an arms race these days as to who can light a car from left to right with no gaps, rendering position markers redundant, and of course blistering white light..

I might just leave them on full time regardless, but it would be nice to achieve a difference between the headlights and the drl.

[Polarsilver]

Garry .. you have convinced me .. given the amount of ignorant Drivers that just pull out from a standing start sideroad, with no consideration of right of way or the closing speed .. happens on a regular basis so has become something i expect to happen .. you probably have highlighted a way to help stop these prats .. let us know the results ..as my only response is the 4 Pot Brakes & give a Good Bast with the Air Horns .

[gs.davies]

Garry .. you have convinced me .. given the amount of ignorant Drivers that just pull out from a standing start sideroad, with no consideration of right of way or the closing speed .. happens on a regular basis so has become something i expect to happen .. you probably have highlighted a way to help stop these prats .. let us know the results ..as my only response is the 4 Pot Brakes & give a Good Bast with the Air Horns .

S Brakes are on the cards for next year.

I definitely need a MUCH louder horn. The standard 850 horn is ridiculously polite.

[snoopy64]

I have sealed beam headlights (utterly useless) but I use a warm white but bright led pilot light, it’s almost as bright as dipped headlights! I switch to sidelights on any major road and dual carriageways.
POS earth dynamo so the led pilot and tail lights draw very little and I can still use the wipers

[MagicWandWoody]

There is a sneaky way to use a single relay to turn DRLs on whenever the ignition is on, but automatically turn them off when the headlamps are on.

Wire a normally-open relay with (A) one end of its coil connected to the aux ign position, so that it gets 12V whenever the ignition is on. And (B) the other end of the relay's coil to the headlamps-out terminal of the light-switch on the dashboard.

When the headlights are off and the ignition is on, the relay sees 12V at one end of its coil while the other end of its coil is grounded (via the headlamp bulb filaments which, when cold, have low resistance) and so the relay is switched on and the contacts are pulled closed, turning on the DRLs. (The current through the relay coil and grounding via the headlamp bulbs is nothing like enough to make the headlamps even glimmer.)

When the headlights are turned on, the relay sees 12V at both ends, so no current flows through its coil, so the contacts open and the DRLs turn off.

This only works if the headlamp switch itself directly supplies the (halogen) headlamps. Any other relay in the headlamp circuit itself will defeat the design.

If the headlamps can be turned on even while the ignition is off, then a diode to prevent current coming back through the relay coil and feeding whatever else is on the aux ign circuit would be a wise precaution to prevent weird behaviour.