Quote:
Originally Posted by Dangerous Doug
I'm thinking regulator, based on the fluctuation I see in the headlight brightness.
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Unlikely. Modern VRs don't tend to "partly fail" - they either quit permitting battery charging (which is the more fail-safe option) so that the power gradually runs down, or they never stop charging the battery, which cooks it. A variation when you rev the engine etc. is more indicative of reduced battery charge, which can be caused by many things.
A loose alternator belt is one common cause. A failing battery is another. Since you do get response at revs, it's likely not the alternator itself. I'd bet on a loose belt, a bad battery, a bad connection somewhere preventing battery charging, or - very last option - a bad regulator.