Electronic speedometer question

["Darren Leung" <destin8@domain.elided>]

I've asked this question before, but got nothing.  Here goes again:
What, if any, are potential causes for speedometer (+odometer/trip) failure?
All other instruments work and the gauge even lights up, but does nothing
while moving.
I don't want to be driving around testing voltages either, as that is clearly
hazardous, so what could cause an issue like this?
The Cardisc shows some schematics that say something about a 'coil'  what coil
is this?  where is it?  what is its function? I'm assuming it's not the
ignition coil, but that could be a bad assumption.

TIA,
Darren
GTV6

--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided