Alternator wiring colours

[Ian and Lins]

This may be the start of a few threads.
The leisure battery doesn't seem to be charging so I thought I'd investigate.
The battery warning light has been missing from its holder for about 3 years, I never got around to replacing it and assumed (as I use the van daily) the battery must be charging. I thought I'd check the bulb holder by putting in the indicator LED in temporarily as I know it works. Turn the ignition on and it did NOT light up. Checked the terminals with a multimeter but no voltage.
There are 2 thick red wires connected to the alternator through female spade connectors and one blue wire ditto. What do they do and what diagnostics can I carry out? I had a look through the Wiki but can't seem to find the advice I need.

[Oldiebut goodie]

I am surprised that your alternator is charging at all without the bulb - that current through the bulb is what excites the alternator into giving out it's juice.
Maybe someone has carried out a modification bypassing it. The blue wire should be carrying 12v from the battery via the bulb with the ignition on and 0v with the engine running (measured across the bulb as the earth is derived from the alternator when it isn't spinning).
Using a led instead of a bulb will not work.

[Ian and Lins]

Ok thanks. Definetely confused now as the battery indicactor bulb is an LED, the same as the oil warning light, high beam and indicator LED. So there should be 12v form the battery through the battery light TO the alternator via a blue cable? What are the red cables for?
Thanks again.

[Oldiebut goodie]

Have a read of this article - it may help (or make it as clear as mud ) Alternator troubleshoot.
Take note of what is said about the wattage of the bulb required to enable the alternator to produce output. That's why a led will not work.

[Ian and Lins]

Hey ho. Sorted the leisure battery charge at leaset. Someone had pigtailed the charging wire together under the van, taped it up and sprayed underseal over it! Corroded through but still held together.