The VW glow plugs are in parallel. I've been known to use an IR
thermometer
to check is a glow plug is working.

Jon

On Thu, 6 Dec 2007, Allan Streib wrote:

> Tabe Johnson <greentabe-vanagon@YAHOO.COM> writes:
>
> > A glow plug is just an electrical resistor.  Imagine a very heavy
> > duty light bulb without the glass globe.  When you pass electricity
> > through it, it heats up.  To check, remove the bolts holding the
> > electric wire to the glow plugs.  Put an ohmmeter between the
> > terminal (where the wire was) and the engine block.  If you get an
> > open circuit (infinite resistance), the glow plug's filament (like a
> > light bulb) is broken and the plug needs to be replaced.  If you get
> > a number like 10 or 30 ohms, (in that range- don't know exactly what
> > it should be) the glow plug is OK.
>
> I don't know about the glow plugs for volkswagen diesels, whether they
> are series or parallel, etc.  But by comparison, on the Mercedes
> "pencil" style glow plugs, the cold resistance of a good glow plug is
> very low, about 0.8 Ohms.  If its much above that at all it is bad; be
> aware that many bargain meters do not read very accurately this low in
> the range.
>
> However, resistance tests are more for identifying bad glow plugs than
> confirming good ones.  A better test to confirm proper operation is
> measuring the current draw as the plug heats up, it will start out
> very high and fall as the plug heats up.  Exact specs are hopefully in
> the Bentley or maybe you can google the brand and type of glow plug to
> see what the current draw should be.
>
> Allan
>