Brake light oddity


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Noticed this a while ago, just decided to investigate. Somebody fitted a high brake light (LED) on the back shelf - good idea, pretty neatly installed. It has a small telltale hole on the inside so the driver can see that its working. I noticed that it comes on when the sidelights are on, and then brighter with brakes on. All the small external lights are LED. On checking I find that there is 8.4V on the brake wires when the sidelights are on. There is one brake feed (GP) on the near side, 2 on the offside. I suspect there is a problem in the near side brake lead, as there is a wire running from the offside brake lead to the near. The 2 brake leads on off side both show the same 8.4V, which is obviously enough to light the high brake light partially, but not the main brake lights.
Thoughts...replace the LED tail/stop lights with normal bulbs, to see if the problem is LED related?
Any other ideas please?


Well-Known Member
Hi, Check and clean the earth points. If a light loses it's earth it can back feed through the other filament to an earth elsewhere. Probably on the sidelight circuit so check the fronts as well.



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I do worry they somehow wired it in series...
"Just take it out of the circuit " - what ? The high stop light?
Yes, will check earths, good point.
Yes. Only it should go dark. If anything else goes dark, that's the source of the fault.


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With the centre stop light disconnected there are no other symptoms - ie the 8.4V is irrelevant, cant go anywhere. The problem with that is I want that light to work the way it should - on with brake lights, otherwise dark. I am currently betting on one of the led stop/tail 'bulbs' leaking.


Staff member
Personally I would take the LEDs out, and fit some standard bulbs to see if that sorts it.

Where is the high level brake wired into?

Mine is wired straight into the trailer take off.


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The high level is spliced (via a double bullet socket) into the nearside connection. Not sure if its related , but the stop/tail connections there seem to be swapped - the bulb socket contact labelled 'T' (Tail ?) drives the stop light , but is on the tail light wire (GP coded), so the wire colours there are swapped. Or is 'T' not what I think it is?


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Success! The LEDs were doing the 8V feed back out the high wattage circuit when the low wattage element was powered. Not only that, one of them was miswired inside, such that the elements were wired on the wrong pins - what I thought was a car problem was inside the bulb. All working properly now with normal bulbs. Fired a rocket up the supplier of the LEDs, but not hoping for anything useful.
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Finally got this sorted properly. Went to my local Jaycar outlet (electrical components, electronics, big range of small bits) with a taillight assembly and one of the questionable LED stop/tail bulbs. They were very helpful - tested my theory (correct), then tested one of their such LEDs, which showed < 1v at the brake light connector when 12v on the side light. Bought 2, all installed and working, no extraneous lights.