LED rear lights

[Dannyb]

Replaced rear /brake bulbs with Led. But the brake lights only work with the lights on.

The old bulbs have continuity between both contacts and the barrel (earth) as expected but also continuity between both contacts. This is where the Led bulb differs.  There's continuity between both contacts and barrel. But not between both contacts.

Danny

 

[Howard]

Danny, LED's are light emitting diodes so when you try to check the continuity there will only be a path one way. So there should be continuity between both contacts and the barrel so what you have measured is correct.

I suggest you try the following:-

Check the power feed to the bulbs. If you have a voltmeter check the voltages on the feed wires to both the side lights and the brake lights (with the side lights off) - you should see 12v in both cases.

Unplug the both wires to the contacts only and with the side lights switched on connect each contact in turn with the sidelight supply - the bulb should light up in both cases. Repeat this with the brake lights & again they should light up in both cases.

I cannot immediately see why you are having a problem, but I know that Triumph did occasionally use a return path through the bulb filament which doesn't work with LED bulbs without a small modification.

 

[Dannyb]

Thanks Howard. I have tried testing as you described above and the bit about the return path seems to make sense as when the lights only are on and the bulb holder removed and the earth wire removed. It still lights, so must be getting a circuit back up the brake wire.

Was this a safety measure if the earth failed or something strange going on.

It's a late spit 1500 and can't see any clue on the wiring diagram. Just wondering if anyone else has come across this and how they got round it.

Danny

[Howard]

I recall Rob Pearce mentioning something similar regarding the indicator circuits at the CT/TSSC meeting so hopefully he will be along shortly with a detailed explanation.

Howard

[RobPearce]

I've encountered almost exactly this query on either this or the TSSC forum, not that long ago. It's different to the indicator question we talked about at the meeting.

There is no intentional "deviousness" in the stop/tail light circuits. The intention is that the bulb is always earthed and the circuits are thus independent. If you have an earth fault (which is very common with those light units) on one side only, the tail lights will still appear to work (if a bit dim) if they are filament ones, because the current can flow through the brake light filament of that bulb to the brake light filament of the other side and thus to earth. However, the faulty side will just "go out" when the brakes are applied. This won't work for LEDs but is, in any case, a fault condition.

Unfortunately I don't remember the conclusion of the previous discussion of LED stop/tail lights but I have a suspicion we concluded the "bulbs" were duff, possibly by design.

Try this: on a bench, with a battery, connect the bulb barrel to negative. Take a wire from positive to each contact in turn. One should light it dimly, the other should light it bright. Then connect the positive wire to both contacts together. It should light brightly. Any deviation from that behaviour is a duff LED bulb.

[standardthread]

I tried to fit LED's our Companion indicators. They only worked when the side-lights were on so I gave up and went back to filaments. I had made a new loom for the car shortly before, based on the late 13/60 wiring diagram, with mods for a fuse box.

[Dannyb]

Sorted. It looks like the earth clip inside the holder needed cleaning and bending to make good contact with the led bulb. The old bulbs are very slightly fatter the the led ones therefore the old bulb had flattened the earth clip. 

Thank all for your help.

Danny

 

 

 

 

4 hours ago, RobPearce said:

I've encountered almost exactly this query on either this or the TSSC forum, not that long ago. It's different to the indicator question we talked about at the meeting.

There is no intentional "deviousness" in the stop/tail light circuits. The intention is that the bulb is always earthed and the circuits are thus independent. If you have an earth fault (which is very common with those light units) on one side only, the tail lights will still appear to work (if a bit dim) if they are filament ones, because the current can flow through the brake light filament of that bulb to the brake light filament of the other side and thus to earth. However, the faulty side will just "go out" when the brakes are applied. This won't work for LEDs but is, in any case, a fault condition.

Unfortunately I don't remember the conclusion of the previous discussion of LED stop/tail lights but I have a suspicion we concluded the "bulbs" were duff, possibly by design.

Try this: on a bench, with a battery, connect the bulb barrel to negative. Take a wire from positive to each contact in turn. One should light it dimly, the other should light it bright. Then connect the positive wire to both contacts together. It should light brightly. Any deviation from that behaviour is a duff LED bulb.

 

[Tim Bancroft]

I fitted LED bulbs to my TR6, ended up having to make separate earth leads for each holder.

[Dannyb]

I still wasn't overwhelmed with the brightness of my new cheep LEDs, plus I noticed a very slight flicker on the side light. So ordered some from Amazon.  What a difference. £15.99 for the pair.

Danny