Should Series light circuits be ignition switched?

scottonthefen · Jul 21, 2019

The side lights on my 2A work with the ignition off.

I can't remember if this was definitely the case before I started tidying up some wiring behind the dash...

The wiring diagram shows the side lights on the other side of the ignition switch, which makes me think the ignition should be on for them to work.

But my brother says the lights on his Series 3 work with the ignition off, and that it's expected as it's an older motor. Leaving lights on used to be the thing you did to drain your battery after all, I did it a few times with my first car in the 90s.

What if anything should work on a 2A with the ignition off?

Colthebrummie · Jul 21, 2019

Just the side lights I think. If hazards have been retro fitted, they will/should work with ignition off too.

Col

Hicap phill · Jul 21, 2019

+1 above.

tottot · Jul 21, 2019

The lot work without ignition on my 2a and 3.

kermit_rr · Jul 21, 2019

Yep only indicators and brake lights come on with the ignition

rob1miles · Jul 22, 2019

Originally I would expect the side lights and headlights to come on without the ignition. Horn usually works to. But it makes sense to wire it so the side and rear come on without the ignition (this may be a legal requirement for stopping at the roadside) but then to add relays for the headlights and take the power for the relay via the ign so you get side / rear without ign but headlights with. Indicators are via ign but hazards must work without ign (again I believe a legal requirment if you have hazards) so you can take the key out and leave them on. A bit of a pain to wire if you want the indicators via ign. If you use relays it makes sense to take the fan and wipers via ign so they can't run too long without the alternator.

blue beasty · Jul 22, 2019

I've had a 2a and two 3's. All lights worked without ignition with the exception of brake lights on one.

Wire it how you like as far as you can be bothered

Colthebrummie · Jul 22, 2019

Someone must have done some rewiring on mine then because my headlights don't work with the ignition off.

Col

kermit_rr · Jul 22, 2019

Even on my modern car i can turn dipped headlights on without the ignition
Don't think I'd want to have the ignition coil heating up just so u can have light

Colthebrummie · Jul 22, 2019

kermit_rr said:
Even on my modern car i can turn dipped headlights on without the ignition
Don't think I'd want to have the ignition coil heating up just so u can have light

When I first started driving, many years ago, a more experienced friend told me that the coil could overheat if I left the ignition on for long periods. So I've always been careful not to. But is it true? How long is too long? How come it doesn't overheat when you drive long distances.

Col

kermit_rr · Jul 22, 2019

I've been told the same, my assumption is the airflow in the engine keeps the temp down, i don't know what happens when it's 'working'

My Old Landy · Jul 22, 2019

My 1987 90 is wired so the lights work without the ignition on. But it's a diesel so coils are irrelevant

The coil overheats because there is no current draw. When the engine is running the coil dissipates heat through energy released.

Colthebrummie · Jul 22, 2019

My Old Landy said:
The coil overheats because there is no current draw. When the engine is running the coil dissipates heat through energy released.

Thanks for that, a it more info for my aging brain cells.

Col

ExMil109 · Jul 22, 2019

When the engine is running, the points are closed about 50% of the time, so the average power into the coil is less. If the engine is stopped with the points open, there's no current into the coil at all, but if the points are closed, current is flowing 100% of the time, hence more heat to be dissipated by the coil. Since you generally don't know if the points are closed or not, it's safer not to leave the ignition on for long periods with the engine stopped.

rob1miles · Jul 22, 2019

Re lights, I got a bit (too) clever and wired it so some things work without ign and some with and used relays to do it, unfortunalty I didn't write down what I did so when I got a loose connection a few weeks ago I was confronted with a mass of wires that I'd fitted and no idea what they did.
Re coil - yes they get very hot - its not just the duty cycle, its because the primary (12v) windings are very low restistance so they pass a high current and overheat, They don't do this when the engine is running becuase there's lots of inductance as the magnettic field builds and colapses and this limits the current.

suburban · Jul 23, 2019

I wired my lights to be ignition on simply to remove the possibility of them being left on by someone, coming back to a flat battery is no fun

suppose you could get all technical and wire in a lights on alarm

scottonthefen · Jul 23, 2019

Cheers all. It's good to know mine's not the only one with side lights that work with the ignition off. I'll leave it as is since I've got bigger jobs on the todo list.

Should Series light circuits be ignition switched?

scottonthefen

Well-Known Member

Colthebrummie

Well-Known Member

Hicap phill

Well-Known Member

tottot

Well-Known Member

kermit_rr

Very

rob1miles

Well-Known Member

blue beasty

Leaks an prone to bits dropping off

Colthebrummie

Well-Known Member

kermit_rr

Very

Colthebrummie

Well-Known Member

kermit_rr

Very

My Old Landy

Keep breathin'

Colthebrummie

Well-Known Member

ExMil109

Active Member

rob1miles

Well-Known Member

suburban

Well-Known Member

scottonthefen

Well-Known Member

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