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Rear Lamps / LED Strip not working


jpwsmith
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Hi all,

I have two issued at the moment.

My car:  Focus ST3 2016 - sorry is the diesel.

1. Drivers side - rear LCD strip (at the bottom of the light cluster) doesn't work - I believe that this is  NOT repairable and is either a dealer repair or a brand new unit all together. can anyone confirm this or advise further?

2. Passenger side - fitted with a twin filament bulb for the rear brakes light and rear lamps/lights (when the headlights are on).  The rear brake filament works files (both drivers and passenger side light up). when the headlights are on only the drivers side rear lamp/light works. I've bought new bulbs and swap them all around between the two sides still not joy - so not the bulbs.  The original bulb had blown hence why I thought, just pop in a replacement as off we go, but this is not the case.

Im thinking might have been a fuse. can only see one fuse in the manual for brakes light and since the bulb does light up when the brakes are applied don't think is can we a fuse issue (unless im mistaken).  Maybe wiring.?!?!?

please help as would like to get this sorted asap.

Thanks .

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On vehicles with the original LED taillights the dual filament light bulbs are only used for brake lights. The 21W filament is used while the 5W filament is not used at all. Instead of using a single filament light bulb Ford used exactly the same dual filament bulb holder and light bulb as the non LED taillights and decided only to use the 21W filament.

The fact that on your driverside taillight the 5W filament of the dual filament bulb is working and the LED light bar is not working strongly suggest that the LED taillight has been replaced with a normal non LED taillight.

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Have you checked for any shorted wires? Might be worth checking the looms. Also as JW mentions, the difference between the LED and non-LED variants is fairly obvious side by side when you look at the bottom half closely. Also the bulb sockets are different between the LED/Non-LED lights as I found out. 

 

You can get the LED clusters on eBay for about £40-50 if you do need one.

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thanks Guys as far as i am aware both rear light clusters are exactly the same.

i have swapped bulbs around  and they all worked as did the LED strip when i first got it.

And on my car there is one twin filement bulb and both filements are used, one for brakes and one when the headlights are on.

i will compare both clusters tomorrow again  but both use twin filement bulbs and both work dependng on whether breakes and / or headlights are on.

20190823_173659.jpg

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you can see if its not led , if they looks same its must be broken , they are quite cheap on eBay.

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Going back to the garage next Friday to get a replacement rear drivers side cluster and will ask them to have a look at the passenger side rear lamps too

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17 hours ago, jpwsmith said:

The rear brake filament works files (both drivers and passenger side light up). when the headlights are on only the drivers side rear lamp/light works

If, as you've said, both filaments are used in the dual-filament bulbs and the passenger side goes out when you press the brake this sounds like a classic case of a broken earth connection.

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before I scrolled down to mjt's post I was also thinking it could be earth problem. to test I would get some wire, strip insulation off ends. wedge one bare end down the side of the bulb in bulb holder so it is touching the metal casing part of bulb, but not the terminals at bottom.  hold the other end of the wire somewhere on the car bodywork where it is bare metal.  Does this make it work correctly?  try both sides of car at the rear lights. easier if you have two people - one for the wire, one to operate light switches.

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1 hour ago, isetta said:

try both sides of car at the rear lights

If it is an earthing problem the break will be on the side that goes out.

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could it still be an earthing issue even though one filament of the bulb lights up and the other doesn't? or am I just being a bit thick, sorry don't know a lot about electrics :(

:unsure:

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Hopefully this drawing will help you to understand how it happens. Notice that when you put on the sidelights there is a current flow through the tail light filament, through the brake filament on the same side and then to earth via the brake filament on the other side. Because the brake filaments have a lower resistance the tail light still works although slightly less bright.

When you press the brake there is now 12V to both filaments and on the side with no earth the voltages cancel and no current flows.

Rear_light_problems.jpg

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Ok so just need to try and find the earthing points then for both the circuits. Like I say brakes lights work but rear lamp doesn't

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Bit of an update.

Swapped the units around. And had a good look at the wiring. It would appear the I have two different units. One has the led strip and other doesn't. The one the dealer fitted was the incorrect type. Going to be an interesting conversation tomorrow with them.

I plugged the left unit into the right and right unit into the left plugs and the rear lamp still did not work. Could this be an issue with the wiring in the light unit itself then rather than earthing?

The plot thickens.

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When you say rear lamp, do you mean the filament bulb for the tail light in the LED unit? If so, then it's as JW said - the tail light for the LED units is just the LED. Despite having a dual filament, only the brake light is wired in the LED lights. 

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The penny drops. Sorry guys. So with the Led unit bulb only come on with brakes and Led is used when headlights are on. So basically the fact the garage has fitted the wrong unit to the drivers side (without led strip) has totally thrown me. Just need them to replace the drivers side unit now then and both should match. Thanks all for your assistance.

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On 8/29/2019 at 10:50 PM, jpwsmith said:

The penny drops. Sorry guys. So with the Led unit bulb only come on with brakes and Led is used when headlights are on. So basically the fact the garage has fitted the wrong unit to the drivers side (without led strip) has totally thrown me. Just need them to replace the drivers side unit now then and both should match. Thanks all for your assistance.

Keep us posted mate, just in case it ends up not being so straightforward.

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