Sidecar lights with LEDs is puzzling

[RogerSB]

Hi Everyone,

Apologies for a long post.

After fitting a Watsonian GP Manx to my A10 and some final adjustments I went for a test ride today (see photo snapped by my wife on my return).  I'm pleased to say it handles a lot better - so now I'm happy with my final settings but I have strange things happening after fitting LED bulbs in the sidecar lights. It has me baffled so I'm hoping someone with electrical wiring knowledge will be able to see what is causing this problem - cus I can't! 

I've been running with LEDs in all my lights on the bike for some time with no problem and after fitting the sidecar and connecting it up to my bike's wiring everything worked fine.  The problem started when I fitted LEDs to the sidecar lights  .

With the headlight switch off, when I depress the brake pedal the stop lights on bike and sidecar come on but the front sidecar light, speedo light and pilot light also comes on. This doesn't happen with an incandescent bulb fitted to the sidecar front light.

Also with LEDs fitted in both sidecar lights if I change the bike's tail/stop light LED to the normal 21/5W bulb the sidecar's rear light doesn't come on. When I put the LED back in the bike's rear light the sidecar's tail/stop light works again but the problem with the front sidecar light, etc returns.

If I change an LED in bike's rear light or the sidecar's front light for normal incandescent bulbs it all works properly.

This is what I've settle for at a the moment: All LEDs, except for one, which is the sidecar front 21W single contact bulb.

Attached are my wiring diagrams, one for bike and showing the sidecar connector added and another showing the sidecar wiring. (I know I could have spliced the earth and the power cables from the sidecar to the bikes wiring but the separate cables were added as a test to isolate the front and rear sidecar lights to try and resolve what was happening.

Thanks for any help, Roger.

[AdrianJ]

I'm guessing that this is something to do with the fact they are Light emitting diodes. Diodes (not light emitting) can easily be used to build logic gates and circuits and I bet you have inadvertently constructed one.
If it's possible you might try reversing a bulb or two and see if that makes any difference. the first one I'd try is the tail/stop. If changing any works you are then into trying possible combinations.
Adrian.

[RogerSB]

Thanks Adrian, my thoughts have been that there is some form of back tracking through the earth wiring, that's why I rewired to isolate the front and rear sidecar lights.  That was before I discovered that if I changed the bike's rear bulb for a 21/5W it threw up a different problem.

The bike's tail/stop LED was from Paul Goff and all the others from Classic Car LEDs and all positive earth.

What seems very strange to me is that the bikes stop light circuit is completely separate from the rest (except for earth).

(Edit) Also my thoughts on back tracking is that LEDs don't need the watts required by incandescent bulbs to work - but how that would cause the problem  .

[chaterlea25]

Hi Rodger
I would check the flexy wire connection from the lamp holder to the lamp base, assuming the lamps have rubber mounted bulb holders
With so little current being used by LED lamps all contacts and connections need to be 110%
so check the brass poles on the lighting switch too

John

[RogerSB]

Hi Rodger
I would check the flexy wire connection from the lamp holder to the lamp base, assuming the lamps have rubber mounted bulb holders
With so little current being used by LED lamps all contacts and connections need to be 110%
so check the brass poles on the lighting switch too
John

Thanks John, Both sidecar lights are new, front is L691, rear is L692, they have rubber gaskets between the bulb holders and GRP mudguard and both have external earth connectors on the rear of the holders with their own earth cable direct to earth on bike's frame. Connections are good (checked them).

Also bear in mind that the stop light switch when activated by brake pedal doesn't go to the lighting switch - it's straight from battery, through stop light switch and stop filament - that's why I can't understand why it's happening and why it also turns on the speedo and pilot light but at the same time it turns off the front sidecar light?

Next plan is to go and buy a LLB245, 12V, 10W single pole bulb from Halfords tomorrow to replace the 21W in the front sidecar light to keep the watts a bit lower for that light - as it's very bright. 10W should be ok, as it's only on when the headlight switch is on and I'm not out much after dark but the stop lights are on and off all the time and so they eat up the amps.  If I, or anyone else can't solve the problem I'll just live with it.

[Bsareg]

My first thought would be the earth to rear stop lamp. The next would be the type of LED used. Some use the same Leds but with a internal resistor to dim the light output for rear light which is by-passed when the foot brake is applied for full output. A bit like a ballast resistor coil set up on a car. This could supply just sufficient current to illuminate other Leds but not an incandescent bulb.

[Greybeard]

By the way, your outfit is very smart! 

[Swarfcut]

 Roger.. My hunch is that the problem lies with the stop/tail lamp holder. Applying the brake sends power through the brake light, then to earth, but a  poor earth on the tail light assembly will mean an easier current path through the tail light bulb circuit, and then back into the rest of the loom. With incandescent bulbs the higher resistance means they don't glow, but with LED's taking a much smaller current to operate, this could explain the phenomenon.

  You sometimes see this on cars, where the brake lights come on dimly in time with the flasher. The earth has failed, and somehow the current finds a way to earth via the other bulb filaments in the light cluster. Common problem with trailer boards which have *** poor cheapo electrics in the way of lampholders and the infamous dirt encrusted plug and socket. 

 See what happens when you isolate the tail light assembly.  My bet is it's our old friend a poor earth.... disconnect the lampholder, and try a jump lead from the tail light lampholder assembly to battery earth.

 Plan B.... start disconnecting additions, testing as you go until you isolate the component circuit causing the problem.

Swarfy

[lawnmowerman]

I'm with Swarfy on this one - check earths and try connecting temporary earths using flying leads between vital areas. It sounds like an obscure fault but this may give you a clue.
Another thing to remember is that LEDs operate at very small voltages in comparison with filament bulbs.
What you may have is various battery voltages (and different earths) at different points on the loom due to voltage drop in the cables and these differences may allow the LEDs to operate.
I fitted LEDs throughout on my Matchless outfit using double LED bulbs on the bike and chair and had no issues but I did rewire it using 2mm cables and 3mm on the earth and battery runs.
Good luck with it.

Jim

[RogerSB]

Thank you all for your help and from some of the comments it does back up my own theory that it's probably somehow earth related due to low current  feedback. Swarfy's first para describes exactly what I've been thinking and that is with a 21W incandescent bulb fitted in the sidecar front light and when the brake is applied the speedo and pilot lights can't come on because they don't get enough current. Without it they do come on because they only need a low current.

At the same time I'm trying to get my head around why the sidecar rear light doesn't come on when I swap the bike's rear LED with an incandescent 21/5W bulb and then everything else works as it should. It certainly seems to point to the bike's rear light but it's hard for me to see why. The bike's earth, which is the bolt in the frame under the seat, I know is clean (only cleaned it with emery paper last week) and all other earth cables are connected to it with ring connectors.

The earth cable from the bike's rear light is a separate cable direct from one of the rear light mounting bolts to the bike's earth, via the fuse to the battery terminal.  I fitted that earth cable in the summer after painting the rear mudguard, number plate, etc. Before that the rear light just relied on the mounting bolt making an earth to the hole in the number plate. All the wiring on the bike has been replaced with new during the last 2 years and the sidecar lights, wiring and connectors in the past few weeks.  It seems my next job is to thoroughly check the bike's rear light connections to eliminate it.

[Greybeard]

Elimination, that's the name of the game!

[RogerSB]

I fitted LEDs throughout on my Matchless outfit using double LED bulbs on the bike and chair and had no issues but I did rewire it using 2mm cables and 3mm on the earth and battery runs.
Jim

Thanks Jim, that gives me something else to consider, as I rewired my bike with a mix of 17 amp and thinwall 16.5 amp cables but used 21 amp tinned for the sidecar.

[lawnmowerman]

I fitted LEDs throughout on my Matchless outfit using double LED bulbs on the bike and chair and had no issues but I did rewire it using 2mm cables and 3mm on the earth and battery runs.
Jim

Thanks Jim, that gives me something else to consider, as I rewired my bike with a mix of 17 amp and thinwall 16.5 amp cables but used 21 amp tinned for the sidecar.

Hi Roger

The current carrying capacity is certainly ok and it sounds like 1mm and 1.5mm for the chair. The main issue when looking at cable sizes on low voltage DC systems is volt drop which is dependant on resistance of the cable which is in turn directly related to cable size. The current ratings given by suppliers should be taken with a pinch of salt - the cables will carry 17.5A or whatever but will have the effect of heating the cable which is energy lost to the bulbs. You may even find that the energy consumed by the cable is more than the energy used by the LED. Modern thin wall cables have an insulation which is more heat resistant than the old PVC insulation which is probably why it looks like you need smaller cables if you are looking at current carrying capacity alone.
It looks like this will be a tricky one to solve and may involve substitution of cables to prove what is going on, and then a new loom to tidy it up.

Jim

[RogerSB]

Thanks again Jim, I bought all my cables from either Holden Vintage & Classic or Vehicle Wiring Products so I'm confident they're of a good quality. My mistake earlier was saying the sidecar wiring is 17 amp, it's actually 21 amp (I stripped it out of a multicore cable I bought but didn't use). Yes, the 16.5 amp thinwall is 1 mm2, 32/0.20 and the 21 amp is 1.5 mm2, 21/0.30.  So maybe even a worse scenario to cause voltage drop. At the moment to get me by I've replaced the front 21W sidecar bulb with a 10W just to keep the amps down.  Now winter is here I only go on short runs once every couple of weeks or so just to keep the oil circulating - so to speak, so I'm now thinking a complete overhaul of the wiring over the winter may be a good idea.

[RDfella]

If you're running LEDs the current draw is tiny, so wire dia is almost irrelevant. Voltage drop can be caused by too small a wire or one that's too long. With LEDs that's definitely not an issue here. 1A wire would be sifficient. What does matter, though, is connection quality. The lower the current, the greater the risk a connection will fail to provide the necessary path. On the face of it, LEDs are a good idea, but I've seen a number of problems when retro-fitting them to bikes, to the extent I'd not bother. They do seem to be very finicky. Maybe as another noted, it's the electronics involved in the bulb.