As the title really, all my lights have had a 'strobe' effect for a while now and i swear its getting worse, its at the point now where the lights on the dash are annoying when driving in the dark. So time to sort it i think, i'm also worried that its a sign the alternator is failing.

Its most noticeable on the instrument lights, headlights and number plate lights.

Its a 91 Polo gt, i went through the paperwork earlier and the alternator was replaced in 03 so is coming on for 10 years old now having done 60k in that time.

Any advice would be much appreciated, i have a feeling i know where some Christmas money will be going...

Also, not sure if its related, but my revs always drop for a moment when pulling away from idle, this has started since the strobing has got more noticeable.

Have you got a multimeter?

Yeah i've got a multimeter, guessing theres some way of testing?

bung the meter on the batt terminals and report back what it says when running , id imagine the voltage reg has failed , they're only about a tenner and easy to fit

Measure voltage with engine off (should be around the 12.0-12.4 mark)

Engine running (13.5-14.5)

If its possible place the multimeter on the main lead out of the alternator and note what the difference is between there and the battery (should be a few .03ish higher there than the battery any more of a drop than a few points could point to needing a new cable (see The Big 3 upgrade FAQ)

Does your battery light come on with the ignition?

Possibly a failed diode? Means a little AC is being put into the battery, hence the fluctuating voltage?

Either way though, sounds like the alt is failing...

If nothing much shows up when you do the above tests, try it with the alternator under load (switch on the lights, blower and rear screen demister.)

A failed diode will cut the output down and MAY be constant, rather than fluctuating.

It would be no bad thing to check and clean all of the alternator, battery and earth connections (If you like, you can check the earth by putting a jump lead between the alternator mounting lug and battery NEGATIVE.) - If doing that with a jump lead cures the problem, obviously you need to then clean up the earth connections.

Regards.

Thanks for the quick reply's chaps, especially on Christmas day, didn't expect that, and sorry for my slow reply! Between doing uni work and with all the family we've had round playing with the polo was frowned upon

So i did the checks, the results were:

With the engine switched off;

12.43v at the battery

12.43v going from the alternators positive terminal to the battery's negative terminal

With engine running at idle;

14.84v at the battery

14.95v going from the alternators positive terminal to the battery's negative terminal

With the engine running at idle but with the heater on full, headlights on, front and rear fogs on and the heated rear window on;

13.88v at the battery

13.67v going from the alternators positive terminal to the battery's negative terminal (this value was jumping up and down though)

Interestingly the 'strobe' effect dissapeared completely when the load of all of the above electrics was added, it reappeared as soon as the heater was switched off.

Not quite sure what this all means, but my values seem a bit high to what you suggested they should be Cymro?

disconnect alt belt and see if it does it? just dont run it for too long, dont want a flat battery obvs

It looks like the alt is putting out full charge. Which means it's working as it should be.

If the strobe effect increases with revs (the flashing frequency increases with revs), it sounds like a little AC is getting into the system somehow.

Which AC won't really damage any circuitry, it will affect normal light bulbs (not the LED type as much). If only one phase of AC is introduced per 3 phases, this could show the pulses you're getting.

When the heater is on, the motor is absorbing the AC like a capacitor, so it disappears.

I guess. Total guess.

Failed diode?