Regarding the glowplug light not illuminating being an indicator of bad plugs, I know that at least on the 60x engines it's not quite that simple.

It says in the manual that if the GP light does not come on, that means the #1 GP is bad, or two or more GPs are bad elsewhere. Meaning that if only one GP (#2-6) is bad, your GP light will still come on.

I'm sure this has changed by 99, but this is how it works on my 87. Figured I'd mention it to see if people can confirm that this is correct.

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon