[Trevor]

Firstly please be sure that I am not trying to extend an argument, but do wish to amplify the detail in respect of that which has proven a never ending problem having considerable technical interest.

The suggestions made here is that a faulty alternator can be detected using a DC voltmeter, because the output measured across the battery, will not be close to 14 volts, if the machine is defective.

It is fact that members here have had an alternator checked by professionals after experiencing the flashing trouble lights problem, then have been advised that the alternator is OK. One would expect that the output voltage has been measured under load by way of a test, but one must presume that the procedure has not detected an AC component in the output, due to only DC test gear being employed.

My contention is that the alternator could produce adequate voltage, albeit at reduced current, even though a faulty diode may exist, but at the same time produce an alternating current component within the output. N.B. --- Hence my reason to dispute the validity of a simple DC voltage test.

The alternator is in effect a three phase device, incorporating nine diodes in rectifier bridge networks, so that the failure of a single diode may only somewhat reduce output current, and the voltage regulator could compensate in respect of voltage.

We need someone who has an alternator with the fault in question, able to carry out proper tests and experiments, in order to be able to exactly confirm the several factors which apply. The understanding required, will likely be above the head of the average auto electrician.