I have just replaced the light bulbs on my Nippy with LEDs from Dynamo & Regulator Conversions and what beautifully bright lights they are now!
However, when the engine is running at low revs the lights flicker strongly, particularly noticeable with the headlights. I have determined that the rate of flicker is related to engine speed and is at the same rate as voltage changes in the electrical system. I can measure the frequency with my digital multimeter.
With LEDs fitted the device carrying the biggest current is now the ignition coil which takes 6 amps with the points closed and the engine not running. So I assume that the power surges to the coil are causing the variations in voltage leading to flickering of the lights.
When measuring the voltage at various places in the wiring between the battery and the terminals for the headlights (the Nippy has a termnal box on the bulkhead to which the lights are connected) I found that the voltage dropped to under 5 volts in spite of the heavy wires. The main culprits are the light switch and the dip switch.
Feeding the coil and the headlights directly from the battery reduces the light flicker considerably.
So the quesion is, how can the voltage be stabilized? Could it simply be that the battery is getting to the end of its life and no longer acts as a "damper"? Or should I fit relays for the lights and the coil so as to isolate the "heavy" current from the switches? Does anyone have any experience with this problem? I'd be grateful for any help and good ideas. Thanks!

Location: Marly, Switzerland

I have fitted relays for the headlights on both my cars to take the heavy current away from the 90-year-old brass contacts in the switchpanel. I discovered the problem when I burnt my fingers on the back of the switchpanel one evening on the way home from the pub, wondering why the lights were rather dimmer than usual. There's no reason why the coil shouldn't have a relay as well. To get as much of your meagre six volts as possible to where they're needed, earth return wires are strongly recommended (rather than relying on the original 'earth return' system). Suitable relays (BG971) here.

David

A true 6 amps is a formidable coil current. Has some low resistance coil intended for electronic ignition found its way into the car?

Location: Auckland, NZ

6 Amps is probably OK if the car is 6 Volt, it would be a worry at 12 volts though.

Location: Rokeby Victoria Australia

I had a similar problem on a Riley Lynx, but there the HT and LT wiring runs through trunking on the engine side of the bulkhead. Flickering was greatly reduced by running the HT wiring outside the trunking. I didn't get around to separating the LT wiring before I sold the car, but I am convinced it was an induction effect from running the wires close together. Other comments about relays to take load off very old switches are sensible, mbut possibly less relevant to the flickering problem.

Robert Leigh

Location: Cottenham, north of Cambridge

I think you should first speak to Classic Dynamo Conversions to see what they recommend, the LEDs are not infallible, I had a problem with light boards in the rear lamps supplied by them, with the side lights off and when the brake pedal was pressed, not only did the brake lights illuminate, so did the front side lights! This fault did not get resolved per se, but replacing the LED front side light bulbs with incandescent has meant that the problem has been overcome, but the problem is with the light board in that when the brake lights are powered, power "leaks" into the side light circuit (obviously the light board provides the common connection). My "fix" has overcome the problem, but clearly, it is not right.

I also had a problem with an electronic flasher from Moss Motors, they supplied 2, both had the same problem in that the LED warning light had a life of its own, they couldn't sort the problem out and gave me my money back.

So, it could be that your LEDs are defective!

In addition, I had a problem with interference affecting analogue radio in my garage (not sure if it affected digital broadcasts) and I would suggest fitting a suppressor to the coil to see if that reduces the interference, failing that, fit a suppressor to each of the spark plugs. You may need to fit a suppressor to the distributor as well.

Do one at a time to see if that improves matters, ignition components should be suppressed in any event to comply with wireless legislation, when most of our cars were new, nothing was suppressed, but this was introduced circa 1930's.

Good luck.

Location: Saltdean, Brighton

"I had a problem with light boards in the rear lamps supplied by them, with the side lights off and when the brake pedal was pressed, not only did the brake lights illuminate, so did the front side lights!"

That usually indicates an earthing problem. I'd suggest that because the LEDs draw such a low current, some was 'leaking' to the sidelights. Because a higher current is required by the incandescents there wasn't enough to illuminate them.

No, it was not an earthing problem, the wiring on my car was all new anyway, tested it on the bench to prove, the fault was on the circuits to the light board, it affected two different types of light board, they seemed to sort out one of them as the replacement was fine, but the other, still unresolved other than my "fix" with using a standard bulb in the side lights rather than an LED.

A problem with the circuitry on the light board.

Location: Saltdean, Brighton

I had the same issue as Gary with the rear LED lightboard. My auto electrician solved it by adding a diode to the lightboard to stop the leakage from brakelight to parklight. Simple fix to a baffling problem which was complicated by my towbar and its attendant trailer lighting circuits. cheers Russell

Location: oz

I have used the combined Tail and Stop LEDs from Dynamo and Regulator conversions. Those supplied to me used a simple series dropper resistor to allow a 3 volt (approximately) LED to be used on 6 volts. Clearly, if the supply voltage varies as the engine revs change, the current through the LED will also vary a bit and some change in brightness will be seen.

One other thing to be aware of is that these particular LED conversions actually had just a single LED, with two different values of dropper resistor joined together at the LED live end. Thus the LED current (and brightness) will be large or small depending on which pin and resistor is being energised. Most of the time this will work as intended, however there is the opportunity for unwanted back feeding, depending on what else is connected to the side and brake circuits.

In my case I had a third central brake light with an ordinary bulb. This was back fed from the LEDs and robbed the sidelight circuit when the brakes were off, leading to no sidelights. I had to solve this problem by adding series diodes to prevent the back feeding before things would work properly. This only came about after a great deal of investigative work and head scratching which I could have done without !

Location: New Forest

David - I discovered the same as you but whilst the car was idle no lights on put my hand behind the switch panel to find it burning hot to touch.
As a result I was looking to replace the switch panel suspecting as you say the 90 year old contacts are failing and could be causing the engine to cut out.
Big panic as I was running the car for a street parade the next day !
But in motion the switch panel didnt get warm at all?
Completely baffled - going for a new switch unit.
Jason