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Alternator/Instrument panel probems

I am having intermittent problems with my alternator/instrument panel on my 10 year old Isuzu LC38.Every 15 minutes or so, the instrument panel warning buzzer 'clicks' rapidly, this progresses to a 'warble' -like a canary. The sound then suddenly stops and the tachometer hand drops to zero. After about 10 minutes, everything returns to normal but the engine revs 'dip' slightly.I have checked wiring , fan belt etc. and when the ignition is on but the engine not started, the warning buzzer and warning lights operate as normal.
Can you help please.

Asked by: Richard Cook  | 7.51am, Tuesday 7 May

WW says:

This sounds as though the control panel is losing the signal telling it that the engine is running. The fact that the tachometer is also affected indicates that it uses the AC signal from the alternator (which drives the tacho) to stop the buzzer when the engine starts. The warbling from the buzzer is caused by the signal coming and going due to the intermittent contact, which will also make the tacho read low.
You probably have a bad connection somewhere between the alternator and the control panel, or within the panel. The wire on the alternator will be the small wire, not the big power cables. Trace the cable route, whilst carefully examining all the connections, and you will probably find the culprit.

Rupert Smedley  | 12.36PM, Tuesday 7 May

If nothing comes to light, the problem might be a bad connection or soldered joint inside the alternator.

Rupert Smedley  | 5.01PM, Tuesday 7 May

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