My mrs has 1.8cvh sierra 1990 hreg, starts runs no problem but battery light comes on when running.

battery doesnt go flat but light stays on, any ideas whats causing it? how to fix it?

Rob

 

i would say alternator fucked, alternator output proberbly either to low or even to high, or it could just be a loose belt,

 

check voltage at battery with engine running should be about 14 volts iff not alternator could be fooked check earths wiring ect

 

It is most likely charging ok, if it stays on permantely even when the ignition is off it sounds like the rectification side is faulty, if not then the correct charge is not being output so as said it's a faulty Alternator or a loose belt.

Alternator on these is Lucas A1 IIRC.

Martin

 

Martin light off when ignition off, only stays on when running.its been like it for 4months or so and battery charging as its not gone flat

 

It sounds like the rectification part, i.e. a loose or a diode gone bad!

You could go on like it for a while or it may fail tommorow, so it's best to get it sorted out as soon as you can, i.e. recon or new alternator.

It may be worth checking the charge output out of interest...

Martin