Buzz & Flicker - Interference or Diodes?

[Monty-4]

Hi,

I've been adding a few things to the car recently to make it a slightly more comfortable daily - a discrete audio system (hidden amplifier with a bluetooth reciever), a cigarette lighter socket, and some LEDs. Unfortunately I'm getting a clicking/buzzing sound from the speakers when the engine is running and the LED courtesy light I've fitted also flickers. I've had two suggestions as to the cause thus far - dead diodes in the alternator causing an AC signal or the need for interference suppressors at the coil and/or alternator. I'm pretty sure my spark plug caps are suppressed already as they are period style 'Lucas LUC1000'.

Context out of the way - a couple of questions:

1. Can I test for dead alternator diodes with a simple multimeter?
2. Am I correct in thinking interference suppressors connect to the +ive side of the coil to earth, and the +ive side of the alternator, to earth?

[TDV102]

I once had this issue and traced it to the dizzy cap! Replaced with a genuine Lucas item and new rotor arm and sorted.

[kennatt]

not sure but I think a diode will alow current to flow in one direction so multimeter would show continuity one way and not the other if ok.but if the diodes had failed you would be having trouble with charging .Also if they have failed and you can use a soldering iron,diodes and charging packs can be bought very reasonable on E bay for the usual moggies alternators, I renuued mine for about £15.

[oliver90owner]

Alternator guess is easily checked - remove the drive belt and check for change!

[bufferzone]

Hello, my LED gauges started flickering after I changed spark wires. I put a ferrite noise suppressor on the power line to the gauges and that fixed it. Might work for you and very inexpensive and easy to do.

[Monty-4]

A quick update on this - my alternator seemed to be on it's way out. The charge fault light came on yesterday (which scared me as I've inadvertantly got the oil pressure and charge bulbs swapped around at some point) and was intermittent, seemingly dependant on RPM but not 100%. I tightened the belt and checked the connections, all fine but it still flickered, so popped to a local motor factors and picked up a new one, swapped it in and all is well again.

They're not as reliable as the old dynamos are they?

[oliver90owner]

Could have been sorted about two hweeks ago, had you simply removed the alternator belt and started the engine as advised. Would have been far better than waiting for a component failure.

Possibly only needed new brushes, anyway. About £1.50? Diagnosis of the fault is usually the cheapest way to go.

Alternators are far less trouble than dynamos and the mechanical voltage regulators, which they replace - and provide more current and at lower engine speeds. I, for one, would not change back to a dynamo, unless for aethsetic reasons.

RAB

[Monty-4]

Indeed. But many other things going on and it wasn't a priority. My partner and I use the car daily so it can be a considerable faff to take it off the road, although I appreciate the alternator may have been doable in an evening.

Now I will have a look at the old one, fix it up and have a spare.