I am having a problem where whenever I turn on any lights other than low beam, a horn sounds. It acts to me like the light is grounding through the horn circuit. This happens with regular high beams, ,the high beam flash function or with fog lights. It sounds just the horn on the passenger side, and dims the headlight on the driver's side. I found and cleaned the chassis ground by the brake master cylinder, but made no difference. Also, swapping around wires on horns made no difference. I have cleaned and re-seated the plugs on both headlights.

This is 1999 XK8 convertible.

Thanks

 

When operating one circuit causes another to go ON or OFF its an earth fault.

 

My wiring diagram shows the lights concerned sharing a common earth point with a horn. Earth point is just below engine bay fuse box and there's another just behind RH headlight might need a look at as well.

 

Or, consider your "combination switch". That was one of the first things I had go bad after I bought my '97 XK8 in 2008....even before the CCTs.

New switch cost me about $225 if I remember, and my son replaced it with a lot of fiddling...and making sure the circuit to the airbag clock spring had NO power. When they start to do strange things, they just get worse. I would hit the turn light lever and I'd lose all low beams. It was a shock as I drove the car home the night I bought it.

Pray for the easiest one.

Ken

 

not to make light of your problem, but does the reverse hold true ?


when you push the horn button do the lights come on ?

Z

 

I found the ground below the fuse box,,, cleaned it, although no signs of corrosion. This did not resolve the issue.

The horn button does not activate the lights.

I am not able to find a ground behind the RH headlight.

I did discover the ambient air temperature sensor is missing. I am thinking the ground circuit could go through this and cause the issue, so have ordered a new sensor.

 

Find the A/C drier, earth stud directly in front of that mounted vertically.

 

See my post above on how to check an earth connection.

 

Not of help but a similar situation...1969 mb 280SL; open left door, turn on key, if the brake level is low an d warning light is displaying...step on brake and the wipers will wipe away until you release brake pedal. This was US model, don't know if they were ultimately repaired or not...but really funny when it occurred.
wj

 

HAHAHAHAHAHA.....good one. Sorry, just couldn't help it.

 

You know, it might be telling if you turn on the lights, horn activates, pull the wire off the horn - what happens to light intensity with loss of ground path through horn?

Yes, how many of you are imagining the windshield wipers activate or the roof starts to open and close? (Ha ha)

 

Okay,,,,it is clearly an earth grounding issue,, however it is not on the ground stud itself, it has to be somewhere in the wiring itself, as all other lights, , ,and the horn work.

pulling the wire off of the horn, the light is very dim, and of course the horn does not work. I have tried disconnecting and reconnecting both horns individually and together.

I am thinking maybe a damaged wire in the wiring harness, the plugs, or the headlight housing.

It appears I need to chase down a schematic,, and break out the power probe.. .was just hoping someone had seen this before. . ..

 

Sounds like the main beam is getting its earth thro the horn . So whichever headlight comes ON with the horn ,however dim thats the one that needs it earth sorted ...

 

And, again....because the hi/low beams is controlled by the "combination" switch (turn signal stalk), the wiring and connections in there should be checked. Gotta be extremely careful if it requires removal; the airbag clockspring must be discharged.

 

Oh god forget the clock spring and all that **** just get in behind the headlight or under the wheel arch and put an earth onto the headlamp bulb that is dim ......KISS

 

My diagram shows LH headlight ground as LF1 which is between A/C drier and RH headlight. That's the groundpoint OP said he could not find and also ground for RH horn.
Might need another look. Seems to tick all the right boxes.

Nyloc nut centre of image is ground point referred to.

 

You dont need to find the original earth just attach an earthed wire to the headlamp thats dim to prove the fault. but I am sure you have found the right earth point.

 

True, this should have been the first step. Oh, well....lessons learned. That's what this forum is for.

 

That's an amazing pic. Do you have anything like that for the underside of the power steering pump and high pressure line connection?

Ken

 

So,,, first, thanks to everyone for their input. I have successfully resolved the issue, , ,and learned a few things. . .

1. That bolt by the A/C drier does not exist on my car.
2. I have never seen where they separated grounds like they do in the wiring diagram for this car. That is why I as having so much trouble understanding what was going on, ,,two different ground connections going to the same light housing.
3. There is no lug or pigtail of any kind, that I could find, on the passenger side of the car. My build date is 7/99, so unless there was a mid-year change in the wiring harness, ,,or maybe a previous owner did a harness change, , ,I don't know.
4. I ruled out the combination switch because I would get the same horn sounding when turning on the fog lights.

Ultimately, I back-chased a ground from the left headlight housing to the ground point below the fuse block on the left fender,, ,and all is good. I hesitated to do this because I hate to put a band-aid on a problem instead of fixing the original problem. In this situation, there is something wrong in the wiring harness somewhere, but this patch is the only way I can see to resolve it.

Thanks again.