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MarkS · 28th February 2021, 02:08

My experience of car electrics is that when you have strange effects, you might have TWO faults that, individually do not have any symptoms, but together, bring up strange symptoms.

Fault 1:
If you have a (marginal) fault, such as a poor connection in the wiring or the bulb holders, of the indicators, you may or may not get a faulty bulb reported.

Because the fault is marginal, a second fault may consistently result in the indicators being reported as faulty.

Fault 2:
If you are getting a reported battery voltage of 12.4 volts while the engine is RUNNING, then you definitely have a charging fault.

The only indication of this fault may be an audible speed change by the fan motor, whenever throttle is applied, and shortly afterwards a dead battery, due to lack of proper charging. So the battery gets changed.

And a reasonable diagnosis would be a faulty alternator, so the alternator is also replaced. As you have done.

So what is the charging fault ?

1) The charging fault may be caused by a poor connection in either the battery or the alternator charging circuit. You cannot assume that because the wires are thick, that there is a good connection.
Faults in the ground connection are often overlooked, and cause difficult to diagnose faults, so the alternator is blamed, and swapped.

2) But if the rubber in the flywheel pulley had perished (and they are all 16+ years old), when the AC is turned on, the (significantly) extra load causes the flywheel pulley to start slipping very SLIGHTLY.

The slipping flywheel pulley leads to a charging fault by the alternator, (but not enough to bring up the alternator warning light). And the subsequent drop in battery voltage causes the marginal indicators to become consistently reported faulty.

Look at the alternator pulley for a (potentially slight) reduction in speed, while a second person switches the AC on/off.

The slowing alternator pulley was initially difficult to see, but as the problem gets worse, a PAS fault may also appear.

And clean up ALL the connections on the indicators. The front ones are very exposed to rain and spray and the rubber seals are probably perished due to age.

28th February 2021, 02:08	#9
MarkS Gets stuck in Rover 75 Diesel Tourer, called Perseverance Join Date: Nov 2011 Location: Bournemouth Posts: 664 Thanks: 189 Thanked 157 Times in 108 Posts	My experience of car electrics is that when you have strange effects, you might have TWO faults that, individually do not have any symptoms, but together, bring up strange symptoms. Fault 1: If you have a (marginal) fault, such as a poor connection in the wiring or the bulb holders, of the indicators, you may or may not get a faulty bulb reported. Because the fault is marginal, a second fault may consistently result in the indicators being reported as faulty. Fault 2: If you are getting a reported battery voltage of 12.4 volts while the engine is RUNNING, then you definitely have a charging fault. The only indication of this fault may be an audible speed change by the fan motor, whenever throttle is applied, and shortly afterwards a dead battery, due to lack of proper charging. So the battery gets changed. And a reasonable diagnosis would be a faulty alternator, so the alternator is also replaced. As you have done. So what is the charging fault ? 1) The charging fault may be caused by a poor connection in either the battery or the alternator charging circuit. You cannot assume that because the wires are thick, that there is a good connection. Faults in the ground connection are often overlooked, and cause difficult to diagnose faults, so the alternator is blamed, and swapped. 2) But if the rubber in the flywheel pulley had perished (and they are all 16+ years old), when the AC is turned on, the (significantly) extra load causes the flywheel pulley to start slipping very SLIGHTLY. The slipping flywheel pulley leads to a charging fault by the alternator, (but not enough to bring up the alternator warning light). And the subsequent drop in battery voltage causes the marginal indicators to become consistently reported faulty. Look at the alternator pulley for a (potentially slight) reduction in speed, while a second person switches the AC on/off. The slowing alternator pulley was initially difficult to see, but as the problem gets worse, a PAS fault may also appear. And clean up ALL the connections on the indicators. The front ones are very exposed to rain and spray and the rubber seals are probably perished due to age. Last edited by MarkS; 28th February 2021 at 02:18..