ron88 Posted April 7, 2015 Report Share Posted April 7, 2015 I bought two LED negative earth RED brake lights. Look great in the running light position but when I hit the brakes, they go out! I switched them, and same issue. Ok, I must be doing simple, wrong. Suggestions welcome. Quote Link to post Share on other sites
marki Posted April 7, 2015 Report Share Posted April 7, 2015 Hi. I had something similar when I changed mine, ended up having to change the number plate bulbs as well. I didn't bother asking why...... Try taking them out and see what happens. Cheers Mark Quote Link to post Share on other sites
rogerowen Posted April 8, 2015 Report Share Posted April 8, 2015 Too much power getting to LED, fit resister in series. Quote Link to post Share on other sites
peejay4A Posted April 8, 2015 Report Share Posted April 8, 2015 i'd be suspicious that your earths aren't too good. I have them fitted and they give no problems and no need for resistors. Quote Link to post Share on other sites
ron88 Posted April 8, 2015 Author Report Share Posted April 8, 2015 I heard about the number plate bulbs - I think I am supposed to take them out and reverse them! Quote Link to post Share on other sites
Lebro Posted April 8, 2015 Report Share Posted April 8, 2015 (edited) I believe it is because you have some filament bulbs installed in the same circuit as your new LED types. I had the same effect when I played with LED tail / stop / flasher lamps last year. They were not as bright as standard ones (TR3), so I ended up using Halogen types, but that's another story. I can't remember the exact mechanism, but it is the ordinary bulbs "stealing" the current from the LED types. Change all to LED's & you should be OK. Bob. P.S. Having thought about it, the solution would be to wire in a couple of diodes eg 1N 4004 or similar in series with the LED non earth connections. ie. one in the brake light circuit, & one in the tail lamp circuit. banded end to the LED lamps. This will block the unwanted current leak which runs from a point inside the LED lamp where two internal resistors are joined, back out of the LED lamp on the other circuit to the filament lamps, & then through the filaments to earth. The current is not enough to light the filament lamps, but it does drag the available voltage at the LED lamps down low so that they do not light up. Phew ! Bob. Edited April 9, 2015 by Lebro Quote Link to post Share on other sites
ron88 Posted April 9, 2015 Author Report Share Posted April 9, 2015 Ok, maybe I will try license plate led's and tail light leds.... seems weird to have to replace a whole "series". Why don't the distributors tell you that? Quote Link to post Share on other sites
Lebro Posted April 9, 2015 Report Share Posted April 9, 2015 The problem is that unlike a bulb which has two independent filaments 6W & 21W, both connected to ground at one end, but on separate circuits at the other end. The LED lamps always use all of the LEDS, but use two resistors to give the two different currents required for the two levels of illumination. The LED's are also connected to ground on one side, but the two feeds (formally to the two separate filaments) are now connected together inside the LED lamp via the two resistors. Bob. Quote Link to post Share on other sites
AndyR100 Posted April 10, 2015 Report Share Posted April 10, 2015 i had this problem on previous car... fitting a couple of diodes fixed it - i agree that the supplies could be a bit more helpful in providing some clues. ...... Andy Quote Link to post Share on other sites
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