Is there any particular requirement for an altenator / battery light, a friend has asked me to wire his new dash and he has an led as an altenator light, I supplied it with a live and connected the other end to the altenator, it does not light, i then tried a standard bulb and this doesnt work either, he has run the car with nothing connected to the altenator, no wires at all, could this have damaged it causing it not to work with the light, when i check for resistance to earth with the car not running there is a resonable amount of resistance indicating whe the bulb / led wont light as it cannot make a circuit, should there be resistance?

 

i may be wrong but its not a switch, its the excitation voltage, i'm ot 100% certain how the wiring works without studying it so i'll let someone else explain...

 

yes i believe that your correct its called the excitation voltage, however for the ign / battery light to illuminate in the first place the altenator must act as an earth? and it doesnt seem to be doing so, however im not sure if a certain rating of bulb is required etc?

 

I think the alternator light runs off a + from the alternator, not an earth mate.

 

prety sure it doesnt, just from my general knowlage and also from looking how my old dash is wired, alt light shares a common wire with the brake warning / handbrake light and oil pressure light, both of which are switched on earth.

 

i think your wiring is right trev, the excitor needs 12v to start the charge process, but remember, your feeding into the diode pack, which can cause resistance, it becomes live alternator end when she starts making charge, so not needing exciting any more, and this also puts the light off

but as a rule, you should never run an alternator unconnected, he may have goosed it, i would imagen a diode failure, due to making charge with diodes not excited(this may also be why you have resistance at the excitor)

 

Thanks James, thats what i was thinking, I have a spare diode / brush pack so I will huck that in and see if that helps.