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S4 Headlight Question

PostPosted: Tue Apr 29, 2014 2:30 pm
by peterexpart
I am confused, on my S4 if you turn on the Headlights before raising them they do not illuminate until they are raised by the Vacuum Switch but if I then push the Vacuum switch off they close into the wings but are still illuminated and remain so until you switch the light switch off, if you then put the switch back to the on position they remain off until they are raised again, is this correct ??

Re: S4 Headlight Question

PostPosted: Tue Apr 29, 2014 4:37 pm
by elanner
Happens on Dip beam only, not Main beam, right?

If so I'll write up the problem/solution. It's interesting but tricky to describe!


Re: S4 Headlight Question

PostPosted: Tue Apr 29, 2014 10:07 pm
by peterexpart
Yes you are correct Dip only !!
Now I am intrigued

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 1:33 am
by elanner
No promises, of course. :-)

The fix for this problem is to rewire the two headlamp microswitches as follows:

Original wiring: One microswitch provides a ground for the Dip and Main relays (BR wire), the other provides a ground for the Flash relay (BP wire).

New wiring: One microswitch provides a ground for the Dip relay, the other provides ground for the Main and Flash relays.

The problem is caused by:
1/ The ability of the blue Main beam lamp in the tacho to provide a ground loop path for the Dip and Main relays.
2/ The holding voltage of modern relays compared with the original relays. Although I've never measured, the original relays must have a holding voltage of more than 6v, while modern relays will hold with less than 6v.

With standard wiring the ground wires from the Dim & Main relays are joined together and then go to a headlamp microswitch. When the headlamp raises the switch closes and both relays are grounded. When you switch the headlamps on 12v is supplied to either the Dip or Main relay, switching it on.

When you lower the headlamps the ground is removed, so the two relays are now simply looped together, electrically in series. If Dip beam is selected the 12v on the Dip relay loops around to the Main relay, through it, and finds a ground through the blue Main beam warning lamp in the tacho. This results in approximately 6v across each relay. This is enough to hold the Dip relay on. So the lights stay on.

If Main beam is selected the 12v on the Main relay loops around to the Dip relay but cannot find a ground path, so the relay switches off. Hence the problem only occurs with Dip beam.

I ran into this problem when I fitted modern, fused, Hella relays. Of course, both old and new relays need more than 6v to switch on, so switching-on behaviour is normal.

In my case I've wired the two headlamp microswitches in parallel in order to increase reliability - if one fails the headlamps will keep working (a link between BR and BP). So my fix was to fit a diode to the Main beam relay where the 12v line from the steering column switch connects (UB wire). Nothing fancy, I think it was rated something prudent, like 20v 3w.

Other ways to fix it would be to find some old relays, or to remove the Main beam warning lamp. ;-)


Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 7:57 am
by Elanconvert
wow nick!!! what I would give for half your knowlege of auto-electrics!!! :shock:

:D fred

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 8:21 am
by William2
I am rebuilding an Elan from an empty shell and boxes of bits. As an electrical engineer myself I have often thought the Elan headlight wiring system is unnecessarily complicated. As I have decided not to have any headlight flasher facility I am going to dispense with all microswitches and use the original relays. All this will make the wiring and installation easier and there will be less parts in the loop to cause any problems. Does this all sound feasible or am I missing something!!

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 8:35 am
by peterexpart
Thank you for that, I will try switching the Earth Leads tonight and see what happens.
There is one other thing that has occurred at the same time as this problem, while putting all the electrics back onto the car after the rebuild I tried each component as it was fitted and the Headlights would only work if the Ignition was on, now they work with the Ignition off !!
Any suggestions ??

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 9:23 am
by lotusfan
To answer the question from William2 about wiring up the headlights without the microswitches or flasher relay - I have done exactly the same. The only thing you are missing by leaving out the microswitches is that it is possible to turn on the headlights when they are retracted. From memory you have to earth a few loose ends that normally go through microswitches but that was easily followed from the wiring diagram.

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 12:10 pm
by Andy8421
As an ex elec eng myself, the wiring of the headlights / flasher / micro switches has always seemed a complete dog's breakfast on the S4 / Sprint. No one ever seems to get credited with designing the wiring on the Elan in the Lotus history books I own, perhaps who ever did it was too embarrassed to admit to it. The unfused ammeter / charging circuit cabling under the dash also makes my hair curl. I am convinced many a burnt out Elan has the poorly designed wiring to blame.
While I am having a grumble, it is giving them far too much credit to call them microswitches. Grotty, cheap, 'spring and a prayer' switches, no weather protection, downright rubbish. In their original application (doorlight switches for interior lights) at least the contacts were protected by being in the door pillar.

Re: S4 Headlight Question

PostPosted: Wed Apr 30, 2014 10:04 pm
by elanner
Thanks for the compliment, Fred, but in truth my knowledge of vehicle wiring stops at Ohms Law.

I was switching to fused relays in an attempt to figure out why my headlamps kept blowing - ultimately traced to the alternator intermittently producing >18v. And the idea of a few more fuses in a high current area where wires are moving as the pods go up and down struck me as a sound idea.

The problem didn't occur with the original relays so I had a good starting point. And fortunately I spotted 6v on the ground wire between the Dip and Main relays. Some pondering over a cup of tea and the wiring diagram revealed all!

The loop exists with original relays too if you leave the headlamps switched on (in Dip position) with the headlamp pods down. I guess it would flatten the battery eventually, but since the sidelamps would also be on the extra drain is presumably irrelevant.

Peter: I have no idea about your ignition question!

I agree that microswitch is a generous term. I did think about fitting a modern switch of some sort (Hall Effect perhaps?) but never put any effort into finding something suitable. Personally I like the idea of the headlamps going off when the pods lower so I didn't want to remove the switches altogether. But having Dip and Main on the same microswitch is simply asking for trouble, so putting the microswitches in parallel seemed like a way to reduce the chances of sudden darkness. Paralleling the switches is not my idea - I saw it in this forum a long time ago.