Lotus Elan

Indicator light in speedo problem

PostPost by: bcmc33 » Wed Mar 14, 2012 6:38 pm

ricarbo wrote:Brian, I should like to think I am wrong, because I like LEDs, with their much improved reliability and lower power use. I'm puzzled that you get the right flashing rate using them, as it is supposed to be affected by the load.
But, I think there may be a problem with using them, from a legal standpoint. As I understand the Road Vehicle Lighting Regulations, you are not going to meet the rules. I've had a look on the internet and have copied the following extract:-

11. Tell-tale?(a) One or more indicators on each side of a vehicle to which indicators are fitted shall be so designed and fitted that the driver when in his seat can readily be aware when it is in operation; or(b) The vehicle shall be equipped with an operational tell-tale for front and rear indicators (including any rear indicator on the rearmost of any trailers drawn by the vehicle).12. Other requirements?(a) Every indicator (other than a semaphore arm, that is an indicator in the form of an illuminated sign which when in operation temporarily alters the outline of the vehicle to the extent of at least 150 mm measured horizontally and is visible from both the front and rear of the vehicle) shall when in operation show a light which flashes constantly at the rate of not less than 60 nor more than 120 flashes per minute. However, in the event of a failure, other than a short-circuit of an indicator, any other indicator on the same side of the vehicle or combination of vehicles may continue to flash, but the rate may be less than 60 or more than 120 flashes per minute. Every indicator shall when in operation perform efficiently regardless of the speed of the vehicle.
I understand this to mean the lamp in the speedo will have to work at MOT time and a failure of a lamp has to alter the flashing rate, but I can't see how your arrangement will do this. You could fix the speedo lamp by running it off a relay easily enough,and maybe your audible device might get you over this anyway, but the other part of the rules would be much more difficult to satisfy. I wonder what they do on modern cars with LEDs - presumably a much fancier electronic flasher unit?

Perhaps I'm missing something, but as I see it, I comply with all the condition of rule 11 & 12. I know I'm a bit thick, but having read the rules four times, cannot see where I don't comply.

I fitted LEDs primarily for two reasons: 1. to make the system more reliable and reduce the current demand on 40 year old cables (this includes the rear side, stop, reversing and front side lights). 2. IMHO, LEDs give better light saturation than filament bulbs on all the individual lamp optics.

Not unlike Alex, I have always been in the Elan driving seat at MOT time so the issue of any of the dash lights not working has never been a consideration of the test.
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(1972 Sprint 5 EFI)

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PostPost by: elanner » Wed Mar 14, 2012 9:02 pm

After my flasher started to fail a few months ago I spent some time trying to get a decent replacement that is reliable, lights the pilot properly and is audible.

After wasting a few bucks buying a cheap unit that proved to be useless I broke down and purchased model 263 (3 terminal, electronic) flasher/beeper unit from http://www.turnalarm.com. This thing has two main features:
- It ain't cheap ($37)

It's a regular flasher with a separate beeper attached to it (across X and P, as far as I remember) in a shrink wrapped package. Perhaps not the most professional thing I've ever seen but the components seem to be of good quality and it's solidly put together. The indicators work, the pilot light works, and the beeper sounds like a reversing lorry/truck. It doesn't appear to be voltage sensitive and, being electronic, I assume it would be fine with LED indicators.

The only problem, for me at least, is that having a beeper/buzzer running on the same duty cycle as the indicators is too much of a good thing. I had to stick some tape over it to quieten it down, which, of course, defeats the idea of having something that is properly audible. I'd like the full volume, but just a click rather than a reversing truck. But it's definitely better than silence.

It's off the bottom of my to-do list, but eventually I plan to strap together a transistor and RC circuit to shorten the beeper duty cycle. Or replace the beeper with a noisy relay/solenoid, if I can find one.

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PostPost by: stugilmour » Thu Mar 15, 2012 4:12 am

bob_rich wrote:Hi (again) Folks...

I sketched up a simple way of overcoming the indicator in the speedo not flashing. A couple of diodes and a resistor ( about a quid from Maplins or $2 from Radio Shack) and then the indicator can be powered from the main lamps this would allow any flasher either 2 or 3 terminal to be used. The parts are small and could be installed with some tape or heat shrink in the wiring. Sketch is for -ve earth For +ve earth turn all diode the other way around.

hope that helps cheers


Perfect Bob. That's the way I did mine on my Plus 2. As it was a total re-wire, I also changed to a modern flasher unit, so the circuit is somewhat different than stock Lotus. I believe my modern flasher used three terminals, but I don't have my wiring diagram to hand to provide more details. Anyway, like Bob says the diodes on the dash bulb method can be used with any flasher configuration.

If you decide to use diodes for the dash bulb, these looked easier to reliably wire than solder and heat shrink. I only found these after I had used Radio Shack diodes, which worked OK as I had the dash out so access was not an issue.

http://www.autoelectricsupplies.co.uk/p ... tegory/123

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PostPost by: ricarbo » Thu Mar 15, 2012 3:20 pm

Sorry Brian, I wasn't trying to be obscure. What I was thinking was that in the event of a failure of one lamp, perhaps your flashing rate won't alter, so won't alert you to the problem. The reason I thought that would be the case is that the current throught the circuit, when using LEDs, won't vary much whether they work or not.
Rule 12 talks about the rate changing if there is a failure, although it uses the word 'may' (meaning 'has permission to') rather than 'must' (meaning 'is compelled to'), so perhaps it is not obligatory that the rate changes. Seems pretty useful if it does, though, and that is how the standard system works on all cars, ancient & modern, so far as I am aware.

I'm still mystified as to how you get the right flashing rate using the standard unit and LEDs. The only way I can imagine it working would be if you added resistors in parallel to the lamps to get the current up, but that of course defeats the current reducing purpose of fitting LEDs in the first place! In the event of lamp failure, the current might still go through the resistor, leaving the flashing rate substantially unchanged. I would have thought the complete solution is a different electronic flasher unit, intended for the job and capable of detecting failure. I don't know of one, but expect somebody makes one.

As to getting through the MOT without a working lamp, I know that they check those on my Toyota, including the lamps that light, then extinguish, on the safety circuits. In order to pass, they check both that it lights and that it goes out, so it won't do to just remove a lamp that stays on, you have to fix the fault.

I agree with the comments about the usual buzzers - terrible racket. A friend has a Caterham 7 with one factory fitted and I find the noise so awful I tend to not use the indicators, which leads to complaints about my driving standards, which are low enough to start with. I home built a different unit for the Elan, using a piezo sounder and electronics which give a short dual freqency tone, which I find much better. It doesn't need to be so loud, because the dual frequency cuts through background noise and the short duration is less annoying. The noise itself is far less unpleasant.
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