How does electrical interference travel?

[Lowbarn]

Could anyone explain in layman’s terms how the electrical interference gets from what’s causing it into my indicator flasher unit?
Is it through the wires or through the ether?
If the wires is it via the negative earth or positive?

Ive just fitted LED lights and they all work perfect apart form the indicator dashboard light. Continuously flickers when the engines running.
I’m standard 6V set up with a dynamo that currently does not work, but that’s another’s thread.

I have tried everything I can see from on threads apart from a capacitor. If that does not work my plan is to completely wire the indicator separately to a second 6V battery. Hence my query about the ether.

Cheers 
Richard.

["Slack Alice" Simon]

Your components like to work on a nice steady voltage - DC.

Because they are electronic, they are able to react to the electrical "noise" generated by the engine's electrical system.

Electronics are much more sensitive to this "noise" -  random spikes of extra voltage, than the old electromechanical components.

As an analogy, imagine the spikes as flash floods running down a river.

A capacitor acts a bit like the flood plains along the river, soaking up the extra volume and smoothing out the flow.

Definitely worth a try fitting one.

Any bit of wire in the system can collect energy from the "spikes", so a capacitor should be fitted as close as possible to the thing you are trying to protect, with as short leads as practicable.

[GK5268]

I can't advise on the electrickery of the interference, but I had similar issue a few years ago when I converted all bulbs to LED, had a similar issue where the warning light indicator continuing to flash after the turn signal was cancelled (and become more rapid...) and some other weird things happening, such as front side lights operating when the brake lights came on. At that time, all the wiring was new, all well earthed, so not a wiring fault.

I fitted diodes to the problem areas, resolved them perfectly. Diodes only allow the current to flow in one direction.

I also have suppressed HT leads to prevent radio interference, the car could definitely be heard on analogue receivers, not sure about digital.

[John Cornforth]

Hi Richard

The short answer is that interference can be both conducted (directly along wires) and radiated (travels through space from one wire and is then picked up by another).

The most effective first step that I have found for stopping odd electrical effects in an Austin 7 is to fit resistive suppressors to the HT leads at the top of the spark plugs. A value of 5000 to 10000 ohms is typical. Without suppression, very high levels of electrical noise are radiated by the ignition system, which will get into all the other wiring of the car.

A capacitor from live to ground at the input to the flasher unit is also worth trying. A typical value would be between 0.1 and 1 microfarad - it's not overly critical. This component effectively shorts to ground any rapid fluctuations, while not affecting steady direct current. Another on the warning light wire might be called for. Mount these components next to the flasher and keep the lead lengths short, say no more than a couple of inches.

[Colin Morgan]

Just asking - could wrapping things in tin foil - NASA style - help?

[Lowbarn]

Thanks for the basic explanations, this all helps figuring out a solution. 

I tried tin foil Colin. Didn’t make any difference. Wrapped the flasher unit.
Sounds like I’m lucky really, because it’s only the indicator dash bulb that’s a problem.
I very happy with the LED’s. Very low battery drain. Means I can use the side lights as day time driving lights. 

I’m now sourcing a couple of capacitors. 

John, are the suppressed plug caps simply the ends that clamp onto the spark plug?
It’s a pity to have to remove the brass nuts, I think they look more authentic.

[Lowbarn]

To conclude this thread I can report that a 0.1 microfarad capacitor on the flasher unit has solved the flickering pilot light issue. 
Tried a 1 microfarad capacitor, but that had no effect.
I haven’t suppressed the plugs.

I have also cured another annoying rattle coming from the front of the engine.
I loosened the fan belt until it’s almost falling off. Still moves air through the radiator, but no longer makes more noise than the tappets.

Thanks for the advice.
Richard.

["Slack Alice" Simon]

Does the top fan pulley move back and forth? - that might be a source of the rattle.

Is the bottom fan pulley loose? - that might be another.

Either of these need sorting, you shouldn't leave them.