not sure if this is the right place for it. (and i have tried to use the search function)

I have a '68 with a bosch altenator attached, and recently while putting a new speedo and external idiot lights in it i realised that...despite the fact that the idiot light acts normally it is not charging

any ideas?

the idiot light is an LED, but i had to add resistance behind it to get it to switch at all. and that seemed fine.....but if i then pull the battery terminal the car will just die

The alternator uses the current through the warning light to excite the fields(?). So if your warning light is blown the alternator will not work. The LED probably is not suppling the necessary current or none at all.

Try temporarily fitting a normal bulb and test with a voltmeter, if you see 13+ volts, (pref 14.2-6 with a charged battery)

yeah i have a normal bulb behind it to create the resistence, thats how i got it to switch at all.


all good thou...turns out it was the brushes, just took the ones out of my car annd hey presto! fixed