headlights staying on even when switch is off

[sideshowme]

(this problem is (perhaps) linked to the thread about indicator switch issues i started previously on another forum... http://forum.ukhac.co.uk/YaBB.pl?num=1287438712)

as mentioned in that thread, my p reg hyundai accent glsi has an issue with the headlights staying on. i *hoped* that it was simply a faulty switch, but replacing it has not resolved the issue. i now hope someone who knows something about car electronics could take a look at the facts of the matter and give some indication regarding how best to go about troubleshooting it as it now seems likely to be a short somewhere in the wiring.

here are the facts (writing them down will probably help me as much as anyone else!):

- the problem started on nov 1st. i indicated left and heard a click when parking up. i thought nothing of it. when i came back to the car a few hours later, the battery was flat, and when it was jump started the lights were on even though the switch was off.

- on one subsequent occasion when i replaced the fusible link, the lights did not immediately go on. however, as soon as i switched lights on, there was no way to switch them off afterwards.

- due to a mix up with part numbers, i bought two replacement switches. i have tried them both, and the problem persists.

- as far as i can see the lighting circuit goes like this:
stalk switch --> [bonnet fuse box] big pink fuse ("FUSIBLE LINK" according to haynes manual) --> 20A RELAY --> two 10A FUSES (one per light) --> lights.

- when the FUSIBLE LINK is removed, it cuts the lights completely. this is how i have been stopping the battery going flat.

- the 20A RELAY does NOT click when the switch is turned, or when the battery is connected and the lights immediately go on. by contrast, the tail light relay clicks when the switch is turned.

- when the RELAY is swapped for another identical one from the same fuse box, the lights stay on.

- when the RELAY is removed altogether, the lights stay on.

- when one of the 10A FUSES is removed, the associated light goes from headlight to parking light (equivalent to one click on the switch).

those are the (puzzling) facts and tests carried out so far.

i know next to nothing about electronics. i'm even struggling to work out whether the fact that the big pink fusible link is the only way to cut the lights suggests that the problem is earlier in the circuit, later in the circuit, or completely irrelevant.

do all the facts give anyone an inkling of where they would start further testing?

thanks for reading!

[sideshowme]

This is a really weird fault

Tracing this fault might require an auto electrician to be honest as there is just something not right with the wiring.

The lights staying on with the relay removed is very strange, unless the relay is a normally closed relay and it has to be energised to switch the lights off

[sideshowme]

This is a really weird fault

Tracing this fault might require an auto electrician to be honest as there is just something not right with the wiring.

The lights staying on with the relay removed is very strange, unless the relay is a normally closed relay and it has to be energised to switch the lights off

that's not good news. it's an old car and so will probably end up being scrapped as it's not really worth the cost of a diagnosis.

my heart did sink when we first noticed the light stays on even with the relay removed. my current thinking is there is a fault with the wiring in the fuse box itself, but unfortunately any efforts to do any more testing have been snowed off...

[sideshowme]

I've had a look on a few Hyundai forums to see if there are similar problems and electrical problems seem very common on several of the Hyundai models and fixing some of the problems is in the £000's

Your best bet might be to give a local auto electrician a call and explain that you don't want to spend a fortune fixing the car and see if he can give you a rough idea of cost before committing to get it fixed.

[Robotstar5]

Sounds like you have 2 faults with the wiring TO the relay, it is not switching from the light switch AND the headlight connections are being bypassed by a short. Can you see the back of the board/box the relays are plugged into?, look for chafed/shorted wires, maybe where they pass through a hole or near something sharp, probably won't be a metal edge or you would be blowing fuses.

[sideshowme]

Sounds like you have 2 faults with the wiring TO the relay, it is not switching from the light switch AND the headlight connections are being bypassed by a short. Can you see the back of the board/box the relays are plugged into?, look for chafed/shorted wires, maybe where they pass through a hole or near something sharp, probably won't be a metal edge or you would be blowing fuses.

having thought about it earlier something similar occurred to me. as the fusible link cuts the lights, but the circuit isn't responding as expected to the relay being removed, the relay must be being bypassed somehow. this suggests (to my limited knowledge of electronics) that the fault must lie somewhere in the connections between the fusible link and the relay. that would appear logical to me. is that the sort of thing you meant?

i was a little confused by "2 faults". as far as i can tell there is no fault with the switch; the switch still functions as expected in every other way, and indeed the problem persists even when the switch is removed from from the circuit altogether. if i've grasped the wrong end of the stick then please explain!

removing the fusebox and looking at the connections would seem to be the next step...

[Robotstar5]

i was a little confused by "2 faults". as far as i can tell there is no fault with the switch; the switch still functions as expected in every other way, and indeed the problem persists even when the switch is removed from from the circuit altogether. if i've grasped the wrong end of the stick then please explain!

Your statement "the 20A RELAY does NOT click when the switch is turned, or when the battery is connected and the lights immediately go on. by contrast, the tail light relay clicks when the switch is turned." would mean to me that although the switch is working correctly, there is a break in the wiring between the switch and the relay (coil connection) as well as a fault with the headlamp wiring "bypassing" the relay (switched contacts)

[sideshowme]

i was a little confused by "2 faults". as far as i can tell there is no fault with the switch; the switch still functions as expected in every other way, and indeed the problem persists even when the switch is removed from from the circuit altogether. if i've grasped the wrong end of the stick then please explain!

Your statement "the 20A RELAY does NOT click when the switch is turned, or when the battery is connected and the lights immediately go on. by contrast, the tail light relay clicks when the switch is turned." would mean to me that although the switch is working correctly, there is a break in the wiring between the switch and the relay (coil connection) as well as a fault with the headlamp wiring "bypassing" the relay (switched contacts)

thanks for your comments. the possibility that the problem is twice as big is quite daunting, i have to admit!

could the failure of the relay to click not be because it has itself failed? i'm struggling to see where the failure might be otherwise, as the switch seems to be working perfectly for all other functions (e.g. the dashboard illumination, which is fused off one of the headlamp fuses between the relay and the bulbs, goes on and off as expected; main beam still functions etc).

my hypothesis (not yet tested due to time and weather...) is that the old faulty switch caused the relay to fail in such a way that it damaged its wiring nearby (some sort of power surge or something maybe?) which has shorted in such a way as to "bypass" the relay. this might be nonsense, of course. the problem has already disappointed me whenever i've tried to apply logic to it...

i notice you're in brum, i don't suppose you know anyone local who is reliable to deal with these things (i'm in brum most days too), as i suspect the job might be beyond my diy skills if there's more to it, and time is running out for the MOT?

[Robotstar5]

Sorry if you already know this, but a relay is used to enable a small switch (eg lightswitch) to switch a high current load (eg headlights)
The 2 faults probably coincide in the area of the relay, from your testing you have power from the fusible link heading towards the relay but not reaching it, instead it is bypassing the relay high current contacts and going straight to the headlight fuses, similarly the power from the switch is going towards the relay coil connection but not reaching it. At some point all these wires are in the same bit of loom which is where the problem has occured. I can only suggest undoing the relay box and look at the loom entering it, split the loom (carefully) with a sharp blade and start tracing the wire colours back down the loom, you will need a circuit diagram to identify wire colours.
Sorry I cannot recommend an auto electrician locally as you can probably tell from the above I do all my own auto electrics and as I'm working 7 days a week at present have little time for my own projects let alone taking on extra work!.
There are bound to be auto electrical forums on the interweb, maybe have a look there?