Sidecar lights with LEDs is puzzling

[RogerSB]

• The earth on the tail lamp fitting (or the bulb) is dodgy OR
• The earth on the side car is dodgy OR
• The tail lamp on the sidecar is reversed (stop <–> tail) OR
• The bulb has dodgy internal wiring – ie coming on more brightly for stop rather than having independent LEDs like they should be OR
• Can the bulbs fit the sockets more than one way? (ie rotate)

Hi Mike, thanks, in answer to the above.
It's a new earth cable from light housing to battery and checked several times during all this.
Same for sidecar.
As previously mentioned I checked both of the rear lights to ensure the correct wiring operates its correct filament both with a multi meter on the connectors in the bulb holders and with 21/5W incandescent bulbs so I could see the filaments.
The red LED tail/stop bulbs don't have visible separate filaments like ordinary bulbs - when I checked they get brighter for the stop light - They were bought from two well known reputable specialist in auto LEDs - and as mentioned earlier changing the bulbs may be worth a try.
No Mike, the bulbs cannot be fitted the wrong way around, having staggered pins.

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[RoyC]

I have got 12v pos E, more or less the same set up as you have and yet all my LEDs work correctly,
My ground wire back to the battery is twice as thick as the other wiring.
I am suspecting one of your LEDs is causing it.

[olev]

Gday Roger,
I think Charter-Lea was close to the mark.
Some LED car brake/tail lights operate off resistors and use the same LEDs for both brake and tail light.
A small resistance (or none) for the brake input (bright light) A large resistor on the tail light input (dimmer light)
I've been fooling around with a Toyota rear light which is configured like this.
As the bike worked ok before the sidecar was connected I'm willing to bet the sidecar tail/brake light is the culprit.
When the brake is pressed, the sidecar brake light works, but also backfeeds current through the tail light resistor into the system.
This will light the other lights you mentioned.
Incandescent lights have a low resistance. If you put one in the bike brake light or the side car side light it will drop the voltage to the point where anything after the tail light resistor won't work.
Best way to test this is to set the machine up with LEDS and remove the side car tail/ brake light.
When you press the brake only the bike brake light should come on.
Replace the bike tail/brake light with the Classic car LED.
If this LED is the cause the speedo lights etc will light when you press the brake.
Be careful using diodes, they drop your voltage .7 volt and you don't have many to play with
Bit long winded but there you go.
BTW nice rig mate,  cheers

[RogerSB]

I have got 12v pos E, more or less the same set up as you have and yet all my LEDs work correctly,
My ground wire back to the battery is twice as thick as the other wiring.
I am suspecting one of your LEDs is causing it.

Thanks Roy, last week I rewired the sidecar, for the second time, checking it for good continuity as I went and used 21 amp for the earth and for the live cables 16.5 thinwall. I've checked all the the wiring on my A10 several times with a multi meter and like you I'm thinking the only thing left is some sort of bulb incompatibility so, in the New Year, I'll go down that route and replace the ones I bought from Classic Car LEDs with ones from Paul Goff and hope that works.  It won't be the end of the world if it doesn't because with a normal 10W bulb in the front sidecar light everything works ok - but I'd like to get to the bottom of it (curiosity) so I'll give that a go.

[RogerSB]

Hi Olev, I was replying to Roy at the same time as you were posting and I think we all came to the same conclusion at the same time.

I think your testing method is spot on (why didn't I think of it  ). Last week (as mentioned previously) as a test, I changed the rear light LEDs around so the one from Classic Car LEDs ended up in the bike and doing that prevented the rear sidecar LED (now Goffy's) from coming on at all but all the others were ok. It was just after I refitted the mudguard and I thought I must have dislodged a connection to that light. I then changed the LEDs back again and the sidecar light came on again. At the time and with all the weird things going on I couldn't understand it and put it down to some sort of problem with the LEDs. What you think is happening would seem to explain it all.

After lunch I'll go out and test it.

[RogerSB]

Here’s the latest and I’ll be as brief as I can to tell the whole story.

All LEDs fitted but removed the one in the sidecar from Classic Car LEDs.
Depressed brake pedal and bike's stop light is working fine. Turned on light switch to pilot position – still all fine.

Took the LED out of the sidecar rear light and fitted it to the bike. Same test but this time the pilot and speedo lights came on again – so that pointed to that LED causing the problem.

Put the LED from Goffy back in bike.

I have a spare white double pole LED (so not a red stop light one) and thought I’d try that in place of the one I removed. Result was same old problem back.

Leaving everything as it is I next removed the pilot and speedo LEDs and replaced them with 2.2W incandescent bulbs. Everything worked as it should.

Left the speedo 2.2W bulb in place but put back the pilot light LED (that consumes a very low 0.08Ah but gives a really bright light for daylight running).  Everything still working ok.

Next I put back the LED in the speedo. Reverted back to the same old problem.

Put the 2.2W incandescent bulb back in the speedo and everything fine again.

So it seems that the problem lies with the LED bulbs and if I have just one (tiny) standard incandescent bulb in the system all lights work as they should.

At the moment I’ve decided to leave the 2.2W bulb in the speedo as that being the lowest watt incandescent bulb only consumes 0.18Ah when it’s working.

[Greybeard]

This has been a very interesting thread. I learnt stuff.

[KiwiGF]

Here’s the latest and I’ll be as brief as I can to tell the whole story.

All LEDs fitted but removed the one in the sidecar from Classic Car LEDs.
Depressed brake pedal and bike's stop light is working fine. Turned on light switch to pilot position – still all fine.

Took the LED out of the sidecar rear light and fitted it to the bike. Same test but this time the pilot and speedo lights came on again – so that pointed to that LED causing the problem.

Put the LED from Goffy back in bike.

I have a spare white double pole LED (so not a red stop light one) and thought I’d try that in place of the one I removed. Result was same old problem back.

Leaving everything as it is I next removed the pilot and speedo LEDs and replaced them with 2.2W incandescent bulbs. Everything worked as it should.

Left the speedo 2.2W bulb in place but put back the pilot light LED (that consumes a very low 0.08Ah but gives a really bright light for daylight running).  Everything still working ok.

Next I put back the LED in the speedo. Reverted back to the same old problem.

Put the 2.2W incandescent bulb back in the speedo and everything fine again.

So it seems that the problem lies with the LED bulbs and if I have just one (tiny) standard incandescent bulb in the system all lights work as they should.

At the moment I’ve decided to leave the 2.2W bulb in the speedo as that being the lowest watt incandescent bulb only consumes 0.18Ah when it’s working.

This is such a long thread I apologise if I am repeating what someone else has said, but here’s a theory, I’ve read somewhere that some “dual filament” stop light LED bulbs light up a proportion of diodes in the “array” for the rear light and all of the Diodes for the stop light, this introduces the possibility of a “leakage” path for current to flow into the light circuit from the brake light circuit. I guess a better design would have separate LED arrays for stop and tail lights.

A test for this would to disconnect the wire to the tail light and see if the problem of the speedo light coming on goes away. The “leakage” might only be enough to power up an LED, not a normal bulb, and this would explain why the issues goes away when the speedo bulb is non LED, but the leakage is still actually happening (even with the lights off).

If this is actually happening the solution would be a different (better) Tail/stop LED, or a separate LED for stop and tail, and new bulb holders.

[RogerSB]

KiwiGF, your absolutely right. I've checked my tail/stop lights and they do just get brighter for the stop light. Initially I thought they may have used separate diodes (see the photos) but Roy reckoned his were not so I checked mine working and and I'm pretty sure he's spot on.

No doubt that it's some sort of back feed through the design of the bulbs, probably via earth and, as you surmise, the 2.2W speedo bulb is enough to stop it from causing the strange behavior.  I intend to makie up a complete set from Paul Goff (as Roy did) and hope the bulb designs are compatible. My bike's tail/stop LED was from Paul Goff and that one didn't cause the problem when I conducted the test suggested by Olev but the other (from sidecar) tail/stop LED did when I fitted it to the bike as a test.

[KiwiGF]

KiwiGF, your absolutely right. I've checked my tail/stop lights and they do just get brighter for the stop light. Initially I thought they may have used separate diodes (see the photos) but Roy reckoned his were not so I checked mine working and and I'm pretty sure he's spot on.

No doubt that it's some sort of back feed through the design of the bulbs, probably via earth and, as you surmise, the 2.2W speedo bulb is enough to stop it from causing the strange behavior.  I intend to makie up a complete set from Paul Goff (as Roy did) and hope the bulb designs are compatible. My bike's tail/stop LED was from Paul Goff and that one didn't cause the problem when I conducted the test suggested by Olev but the other (from sidecar) tail/stop LED did when I fitted it to the bike as a test.

I’m glad it helped, but one thing, I’m not suggesting the leakage from the stop light circuit occurs to earth, but into the lighting circuit, although it may only be the speedo bulb lighting up when it shouldn’t I’m suggesting all the bulbs in the lighting circuit (that are switched “on” by default) are getting some leakage current from the stoplight LED/circuit, on most bikes the default will be just the pilot light and speedo, and for those without a pilot light the dip or main, instead of the pilot light.

As before disconnect the wire feeding power to the tail light and the leakage into the lighting circuit would stop, if my theory is correct.

[RogerSB]

As before disconnect the wire feeding power to the tail light and the leakage into the lighting circuit would stop, if my theory is correct.

Thanks KiwiGF, I'll give it a try today.

[RogerSB]

Just carried out the test that KiwiGF suggested and he’s definitely on the right track but the electrickery still won’t give up.

I put the LED back in the speedo again, disconnected the live feed to the sidecar tail light and kept the stop light cable connected (just in case anybody queries it, they are in separate bullet connectors).

Turned the pilot light on, speedo and bike’s tail light on and no sidecar lights - so that’s good.

Turned the light switch off and pressed the brake pedal, both stop lights came on but no pilot or speedo light    that’s it! I thought . . . then I noticed the front sidecar light was also on. 

Next I disconnected the bike’s tail light (so both tail lights now disconnected). Result was the same as before (apart from, of course, the bike’s tail light).

So KiwiGF is right in his thinking but even with the live cables to the tail lights disconnected somehow there's enough current getting to the front sidecar light by operation of the stop lights.

I've put the 2.2W incandescent bulb back in the speedo and its now giving off its heart warming, dim, warm glow and all the horrid LEDs are happy again.   

[Greybeard]

So, is that how things will remain?

[RoyC]

So, is that how things will remain?

Yes, until they change.   

[RogerSB]

So, is that how things will remain?

I suppose so Neil, at least until after the New Year when Paul Goff has all the bulbs back in stock I'd like to try.

Took the outfit out for a run this afternoon for a few miles. Mainly to test it two up, first with my wife as pillion and then back with her in the sidecar. She said she preferred the sidecar but only because she didn't like the feel of the bike going around corners with a sidecar attached, i.e. not leaning into a corner as she's used to it doing.