To learn more (perhaps more than you really wanted to
know) about the VW diesel glow-system, visit Roger
Brown's excellent page:

http://4crawler.cruiserpages.com/Diesel/CheapTricks/GlowPlugs.shtml

From whence I quote:
"So you have the little yellow glow plug LED on the
dash, why do you need another glow plug light?
Actually, the LED on the dash has nothing to do with
the glow plugs. Its just an output from one part of
the glow plug relay, which takes the temperature
sender input and produces a delay to let the glow
plugs reach the proper operating temperature. The glow
plugs themselves are powered by a relay which is
operated by a different part of the relay circuit and
they generally stay on for a time after the LED goes
out. If the coolant temperature is warm enough, the
glow plugs and LED won't be turned on at all in the
"glow" position of the ignition switch. However, the
glow plugs are always turned on whenever the starter
is operating, regardless of temperature.

"By running a wire off the glow plug bus bar to a
light on the dash, it will be possible to observe when
power is actually reaching the glow plugs directly.
This indicator would be useful to diagnose a number of
glow plug problems."

IIRC, the Bentley specifies that--assuming a cold
engine--the glow plugs should continue to glow for 30
seconds AFTER the engine is running, although the dash
indicator will have gone out long before.

Jeffrey Earl
1983 diesel Westfalia "Vanasazi"

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