Electrics: Unusual headlight issue

[RowersS40]

I've got an unusual headlight issue and none of the other topics/fixes seems to have fixed the problem. 1998 S40 1.8i:

After starting both headlights are on but extremely dim - unusable at night. If I play around with the headlight angle switch, move it from 0 to 3 and back, 'normal' brightness resumes in one headlight (nearside) and nothing in the offside (initially this made them both work but no longer). If I switch on full beam, offside works, nearside has nothing. I've also checked my sidelights which also don't appear to be working at all.

So far I've checked the alternator but that appears to be working - 14.5V measured at the battery with every electrical item on and engine running. I've checked the bulbs and they're fine. The fuses must be OK as power is getting through to the lights?

9 months ago I had the whole nearside headlamp assembly replaced as the output no longer met the new MOT regulations. This issue didn't start immediately after, I only noticed in the last couple of weeks.

Any ideas?!? It does have intermittent power loss whilst driving, rather sporadic, but I've assumed that's not related (although there are some posts that suggest otherwise) and put it down to my oil leak (which only appears when driving) and/or any number of other things. It does occasionally also need a boost to get it started, which again is sporadic, sometimes occurs after a long drive, hence my initial look at the alternator. Generally, 15 minutes with a solar panel fixes that.

During my tests today I also heard an odd "sparking" noise, without the engine running, whilst trying to resolve my headlight issue.

Thanks!

[Thassos]

I would have a look at the chassis / negative return to said headlights, if you have a DVM, try measuring across the bulb connection with the bulb connected and ON, you should be seeing roughly the same as the batt voltage measured across the battery, if its lower then you have a volt drop somewhere, measure then from the batt negative to the (negative) side if the bulb, you shouldnt see anything but a very small voltage difference, easily sub 0.5v im guessing.

Often a poor connection on a chassis (-) connection to the headlamp module can cause this kind of problem and often youll see other bulbs not working as expected in the same headlamp..

[RowersS40]

Thanks Thassos:

Battery ~11.8V

Offside lamp, when dim ~ 8V
Offside lamp, when nearside bright, i.e. after fiddling with angle to "fix" brightness ~ 10.9V

The offside lamp goes off as soon as the angle has finished moving all the way down.

I didn't measure the nearside as it's a pain to access due to the battery.

So this suggests the poor connection? Is this a fairly easy fix for a mechanic? Or it could it be somewhere else in the loop?

[RowersS40]

Just did the second part of your test, around a 0.2V drop between the battery and the negative of the bulb when it's dim.

[druid]

Earth! It has to be.

[Thassos]

Hi Rowers,

Well thats a good start, fault finidng is all about a logical step by step approach until you've exhausted all the possibilities, at which point you
begin to wonder..

Well it sounds like the poor chassis conn it isnt, so next step is to make a similar volt drop measurement between the battery positive and the + side of the not working so well (bulb) NWSW from here !

I was trying to find an old manual with the S40 wiring/circuits to post but so far has eluded me (but ill keep looking!)

Generally from the battery +side, you go thru a very big fuse, and then to the fusebox, or for things switched on with the ignition this would be the first switch in the line, then perhaps returning to the fusebox and then out thru individual lower current fuses to the actual NWSW part (often a secondary switch like say the headlamp switch that also needs to be closed to allow voltage out to the NWSW part).

So quick first step is measure from battery +v to the positive side of the NWSW bulb for instance, you should be seeing less than 0.5v drop here (with the bulb lit) or less as this side comes thru several fuses & switches you could expect a slightly bigger drop than on the chassis side,..

You mention things cutting out, so this also could be indicative of a poor positive feed on the battery + side, so ild be looking for corroded terminals or water ingress, try pulling spade type connections off, and pushing them back on a few times or using fine wet n dry on any corrosion or oxidised terminals (dont go mad just enough to remove the offending corrosion)

Anyway let me know how it goes, and ill try to assist, post any pics you can, it might help in figuring out your problemo...

[loely]

When having 8 v over the bulb try messuring over -at the bulb and - at the batt (at the batt itself not the cable connection) .
If there is a diference you have a faulty mass at the batt or the chassis where - cable is fixed.
Try a direct -wire from batt to bulb when no change try the same withe the + .There sould be a difference in one off the cases. At least you should know if it is a mass or current problem and go on frome there.

[Thassos]

Found the info.. try checking the voltage working from battery thru fuse, to the headlamp relay (a likely culprit) post your findings added some arrows on the 002 diag to assist.

[RowersS40]

Originally Posted by Thassos

Found the info.. try checking the voltage working from battery thru fuse, to the headlamp relay (a likely culprit) post your findings added some arrows on the 002 diag to assist.

Thanks Thassos, for some reason the forum stopped sending me emails when replies were posted... I'll take a look at this when back from work, along with some pictures. What does NWSW mean?

[RowersS40]

Thanks for your help Thassos, loely, it's extremely appreciated!

I realised when I provided the voltage readings previously I couldn't be certain I got the correct pin on the bulb, so I've provided every reading I can think of(!). When I refer to "left" and "right" pins it's from the perspective of the back of the bulb where you attach the connector, but that will probably be obvious to you:

Battery: 11.98

Negative to top pin: 0
Negative to right: 8.47
Negative to left: 11.72

Positive to top: 11.67
Positive to right: 3.5
Positive to left: 0

This is also whilst the bulb is still dim. I've not had a chance to test to the fusebox/switches yet - the engine was still a little warm! Two other observations:

1. When I first put the voltmeter across the battery and the light it sounded like the gear to change the headlight height came on briefly

2. Towards the end of my investigation, a noise came from what seemed like the back of the engine (towards the windscreen) that sounded like another motor or something electrical but I couldn't trace it.

I took some photos, no idea if they'll be useful, I'll try to post them in a minute!