No Battery light with ignition

[Mikieb1981]

Trying to get to the bottom of my mates trucks charging problems.

Battery went flat a week or so ago, put new battery on and checked with meter no charge coming from alternator.

Replaced alternator with a new one and still no charge, remembered reading a post on here about battery light and checked it to find its not on. 

Checked bulb and its fine, checked continuity on all the alternator wiring to instument panel and battery and all seems fine. 

Checked voltage at the battery light with the ignition on and it has 12v to both sides which expalins why it doesn't light up.  What I don't know is why and what is causing the voltage?

Anybody got any ideas??, I think it was the same with the old alternator so is a fault on the car rather than a bad part but if no other ideas i'll double check with a know good alternator (mine!)

HELP!!

[JIMBOBLY]

yeah,i did mention it myself about no light no charging on mobi's post,if you are gettin voltage both sides as you say,its back feeding by the sounds of things,which i'd say is the earth from engine to chassis,but,be very careful with what tester you are using,this may sound odd,but if you are using a led tester,they will pick up the slightist of back feeds,if you are using a tester with the sharp probe,always use a bulb tester,you might know this anyway,hope this may help.

[Mikieb1981]

Cheers guess if its feeding back I might be able to trace the wires back and find the source.

Am just using a run of the mill multimeter on dc volts reading from the ribbon to ground and gtting a definate 12v.

Looks like a bit of head scratching this evening when i've finished work!

Oh meant to say its a 1990 200 tdi.