Instrument lights pulsing

[Steve Simpson]

I dont remember seeing anything previously about an issue I have with my instrument lights. When I start the car the instrument lights and radio display pulse bright and dim every couple of seconds. The main lights may do the same but it is hard to tell as I have only been out recently when dusk. The car is stored with a accumate battery conditioner when not in use. I am sure I noticed this once last year but it dissapeared after the car had been running for a few minutes but it seems to have done it for the whole of my recent trips out (15/20 miles duration). Is this normal and could it be causing any other problems. The car runs well other than surging when cruising on light throttle at lowish speed (some say they are all prone to that to a degree....another and wider topic i'm sure!!)

Another problem I have found recently is extreme tiredness. Me that is not the car!! As a newcomer to these forums I have found them addictive (several late nights later) and thanks to everyone I have learnt loads most of which I hope I will not need to know and I am only up to page 50. All I can say is thanks for a fantastic facility and I look foreward to helping someone one day with a gem of wisdom from my limited portfolio of experience.

[apache]

I'd say your alternator is due for a change

[paulathome]

Hi Steve. If your lights are pulsing in brightness it sounds like a poor earth or your alternator bushes
are on their way out. The brushes are an easy option to change, check them first.
Check chassis to engine cable is nice and tight and the live to battery is ok, and of course the 100 amp fuse on the chassis rail (if fitted)is not rotting away.
My neighbour had a similar fault on his golf and it was a loose earth to the engine.

Try and find it sooner rather than later because if you loose the earth completely the voltage from the
alternator will shoot sky high without a load. That doesn't bear thinking about especially the ECU and the damage to
other voltage sensitive electrical devices.
Hope this helps.
Paul.

[Cider Andy]

I'm with Apache, it's almost certainly the alternator failing to regulate the voltage properly and probably pushing it too high. I'd have it checked by an auto electrician, because if it is doing what I think it could well cause expensive damage to the ECU, as paulathome says.

[gsw500]

Steve,
I have a thread running about this problem too on the griff forum headed 'new battery advice needed'.
I have a similar prob to yours and I would suspect your front and rear lights are pulsing with everything else.
I seem to have a pulsing of the engine too on idle is that the same sympton as yours..?
Could the alternator affect this...?

So guys if the alternator is on the way out can the spikes of higher voltage say as mine up to 16 volts do serious damage to the ecu.
My voltmeter on the dash tells me the returning voltage to be just over 15 volts but when checked with multimeter the readings were not at a constant but ranged between 11 and 16 volts.
I found if I drove with the lights on even during the day the voltmeter would hover around 13 volts.
Problem now is battery is losing charge over night.

Any ideas.

Cheers.

Gsw500

[Steve Simpson]

Hi Gary
The idle speed does not seem to vary with the pulsing (only surging at low load as previously mentioned) and I will try the lights in the garage tonight after dark to see if they are pulsing but I suspect that they will be. I would assume that changing the alternator brushes alone would not stop the variance in voltage but electrics are not my strong point. I'll take off the alternator and have it tested later in the week. I,ll keep you posted. Thanks for the advice so far folks. Any other feedback from anyone with similar symptoms greatfully received. I,ll not drive it untill i've got to the bottom of things as I don't want to mess up the ECU

[russ_chim]

I have just noticed the same problem and happened to be over at TVR Fix yesterday so I asked the mechanic. Apparently it is caused by a unit within the alternator which regulates / smoothes out the voltage, as a number of others on this thread have already alluded to. He checked that the alternator is still producing a good charge to the battery (which it was) and said that I should not be too concerned. But obviously if I was bothered I should get the alternator refurb. The dash lights run off a low voltage and are the first to show any variance.

I'm no auto electric expert and I would be concerned about any potential damage to the ECU, however since the ECU draws charge off of the battery would it be affected by a variable charge going into the battery?? Have no idea.

Hope this helps

Russ

[apache]

russ_chim said:

I have just noticed the same problem and happened to be over at TVR Fix yesterday so I asked the mechanic. Apparently it is caused by a unit within the alternator which regulates / smoothes out the voltage, as a number of others on this thread have already alluded to. He checked that the alternator is still producing a good charge to the battery (which it was) and said that I should not be too concerned. But obviously if I was bothered I should get the alternator refurb. The dash lights run off a low voltage and are the first to show any variance. I'm no auto electric expert and I would be concerned about any potential damage to the ECU, however since the ECU draws charge off of the battery would it be affected by a variable charge going into the battery?? Have no idea. Hope this helps Russ

In the old days you could get your alternator refurbed and have a regulator pack fitted if trhe old one was duff. Nowadays I suppose you have to bin the whole thing

[gsw500]

Apache,
I'm sure I've been told that it is poss to have the alternator refurbed including the 'diode' pack hope thats right cos bloke down the pub said so. Have also been told the alternator should at most be pushing 14.7 volts back to battery.. Maybe a techie could put us straight on that one.
I might be a sparks but am used to dealing with 240/415V

To be quite honest I really don't want to chance it so will be fitting new 100A Marelli unit on tues.
Will post up results after to let both Steve and Russ know outcome.

Cheers.
Gsw500

[Cider Andy]

gsw500 said:

...can the spikes of higher voltage say as mine up to 16 volts do serious damage to the ecu. My voltmeter on the dash tells me the returning voltage to be just over 15 volts but when checked with multimeter the readings were not at a constant but ranged between 11 and 16 volts....Problem now is battery is losing charge over night.

Some electronic devices are very tolerant of fluctuations in the supply voltage, others less so; I have a GPS device that will work perfectly well on any input voltage between 9V and 30V, so is very tolerant by design. The ECU ought to be ok up to at least 15V, as it is quite normal for the battery voltage to be at just under 15V with the engine (and therefore the alternator) running, but beyond that, I don't know. Your battery losing charge overnight could also be caused by a faulty alternator, it's probably a good idea that you've bought a replacement.

gsw500 said:

Have also been told the alternator should at most be pushing 14.7 volts back to battery

Yes, that's right.