My XJ is an LED Xmas Tree!

Any wiring experts out there...? I replaced some dash globes on my XJ with LED's to reduce the load on the battery (had a problem with indicators not flashing at idle when the headlight was on for a while).
So...I replaced the lights in the speedo & tacho housing with blue LEDs, the 2 dash indicator lights with yellow LEDs, and the neutral light with a green LED.

All worked perfectly.Too perfectly. All lights off - right...it seemed that when I applied the front or rear brake not only did the tail brake light come on so did all the others - speedo/tacho/sidelight in the headlight shell. I traced the problem to the LED in the speedo housing. Once I took this out the problem didn't occur. Couldn't get around it though so put back the original little dash lights.
Can anyone explain why the LEds had this effect. They came as complete units with the resisors built into them. They are T10's - got them here at this site:
http://www.ledshoponline.com/automotive_leds.htm

 

The symptoms would suggest a short with the brake circuit feeding power back into the loom, but since all works OK with the normal bulbs? and the brake light circuit should not effect the other lights??

Did you try swapping a different led to see if the problem was just 1 individual LED or if any of them in that one position would cause the fault?

As for you original problem are your alternator brushes within spec and the rings they run on clean and in good nick? All your connections tight and clean? Alternator output OK?

 

Re Alternator brushes. Within spec, yes, well above the marker line. But they were in the bike when I got it a couple of years ago and I think I read it on this site somwewhere that even though brushes can be within spec on their length they might actually lose some of their "oomph" (technical term) over time. A new set will be swapped in before our (southern) summer starts.
Didn't try using another LED to see if that one particular LED was the problem but might give that a go next weekend. All works fine with the normal bulbs but the LED's, im particular the one in the speedo housing, was the one causing the dash lights to come on. A curious and wonderful mystery. I did notice however that when I was inmserting the LED's that they only worked one way - that is after initial insertion into the socket, if they didn't work, I had to rotate it 180 degrees to make it light up. Do they have a polarity thing happening with LEDs?
My mission, should I accept it, is to get to the bottom of this mystery...

On a related note, I think the old flasher units don't cope with the load with the headlight on but I believe a car type 3 prong electronic flasher unit might be the ideal solution to this problem of current draw.

 

LED = Light Emitting Diode. A diode is an electrical one-way device, thus the device only conducts in one direction depending upon polarity observation. I haven't time right now to expound further but I will get back to you on this issue.
TTFN.

 

A led is a diode (light emiting diode)it only allows current to flow one way,it is very possible that you have a small backfeed somewhere it doesnt take near the juice to light up a led

 

Which bike is this issue occuring on?
I noted that the web site your link directed me too advertised a flasher (out of stock at this time, bummer) that is supposed to be used rather than a standard bi-metalic relay to help your flasher system work correctly. Remember, the LED set up isn't going to put as much a load (even with the voltage dropping resistors in place) on the relay system and will not trigger the stock flasher.

 

Here's the link for the main page and then there's a box for the T10 dashboard lights:

http://www.ledshoponline.com/index.html

I have a 1985 XJ900 - same as the '83 but the only difference I can work out is that the '85 is 891cc or thereabouts whereas the earlier model was only around 853cc. But it looks like the wiring diagram in the Haynes manual is pretty common to both.

See how you go with the above link this time.

KarlH

 

Robert, I believe redcentre003 has only replaced the dash lights with LED's not the signals.

redcentre003, did I read your first post correctly, only the dash lights were switched to LED's? I'm assuming the signals are still stock?

 

Sorry mate, I've not got the required schematic so I'm not going to be too much use in tracking down the problem.

 

In response to the question of which lights I replaced...it was only the dash lights that were replaced; i.e. right & left indicator dash lights and speedo & tacho lights within the housings.

I did not replace the actual indicator/turn signal bulbs - they are still stock standard normal filament bulbs.

And it was the little LED in the speedo housing that seemed to have the effect of causing the dash lights to come on when I depressed the brake lever(s). I swapped some other LEDs in it's place and the same happened - i.e. it wasn't a defective LED bulb. Must be something to do with polarity and completing an electrical circuit. The wiring diagram in Haynes shows that there is a common wire from the brake switches around and through the speedo and tacho, albeit an earth wire from memory but I'll have to check.

 

first let me say I'm not a electrical wiz,I can figgure it out if I'm looking at it but trying to disagnose online isnt my strong point,however,being as a led is a diode only works with current flowing one way,I cant see how a backfeed on a ground would light it up or how it would allow current through to light up other led's?? it would have to be allowing a small amount of current to travel down the pos wire,I say a small amount since you dont have problem with regular bulbs,led's dont take as much current to light HMMM :?

 

I'm trying to work this in my head,does it make a differance if its the front brake or rear brake?if both do it try pulling brake light bulb and see what happens

 

Same thing happens whether it is front brake or rear brake pedal/switches.

Haven't thought about pulling a rear brake light bulb but will give that a go. Might pay to not that a few months ago I replaced the 2 normal twin filament brake light bulbs with 2 x LED cluster bulbs. They have been working fine.
I'm no electrical woz either but the only thing I can think of is polarity. With the standard dash bulbs it makes no difference which way you slot them in to the holders, but the LEDs are fussy in this regard.

 

I believe we are thinking along the same lines,I dont have a wiring diagram so I'm trying to picture where you could get current flowing in correct direction,and the rear brake light tail light assy is about all that is coming to me,my thoughts are is it somehow getting juice from brake light circut to lighting circut??

 

I think your problem is there when you have the standard bulbs in dash ect ect,its just not getting enough current to light standard bulbs,but it is enough to light LED's.


We know with led's current has to be flowing correct direction,so the ground or earth however you say it cant be where the current is coming from,without a diagram or being able to actually see bike the taillight assy is still only place I can think of that current could be bleeding off brake circut to lighting circut?? possibly a connector or bad spot in wiring too,I think if you keep looking where brake circut and lighting circut are together you will aventually isolate where the current is bleeding

 

These strange wrong lamp lighting issues are often a sign of a poor ground (earth). Not enough bleed back to light a standard bulb, but enough to light a LED I expect.

 

Thank you all for your contributions on this matter.
I'll do some wiring detective work on the weekend and see what it yields.

KarlH