Alternator Warning Light Wiring

[Fylnn]

I have replaced the gauges in the GTV6 with VDO's and replaced the whole central instrument pod.  To get the alternator warning light, I cut the alternator wire and the wire from the ignition that went into the warning light and plugged them into the back of an LED pilot light in the dash.  That seemed to work OK for a while.  But then I took the heater box out recently and disconnected the fan and the resistor block for the fan that sits on the RH guard in the engine bay.  When I did this the alternator warning light I wired up no longer works at all. 

Anyone got any bright ideas or actually understand the principle of how alternator warning lights work?  It seems there is a hot wire from the ignition on one side and a wire from the alternator on the other and somehow it lights up with the alternator does not produce power.  But I can't for the life of me work out what I took out in the heater that would have affected this. 

[colcol]

From what i can remember the Alternator warning light glows when power goes from the battery to the Alternator, that is the battery is being discharged, when the Alternator is charging the battery the power goes the other way up the Alternator wire, and the light doesn't glow, thats why old school cars like my 33 the Alternator light glows when i pull up at the lights with its small 45 Amp output, with my 156, no such drama with its [i think] 120 Amp output, Colin.