Alternator Charge Light

Back when I first started the engine I checked the oil pressure light and charge lights were going out once the engine was started. The oil pressure light went out showing I had oil pressure and the wiring was correct. Sadly the charge warning light connected to the alternator stayed lit. So stuck it on my ToDo list and got on with more fun stuff like getting the clutch fixed :-)

So why is the charge light staying on when the engine is running. Alternator is new, but could be faulty or my wiring. Turned out to be neither.

I understand that one side of the light has 12v and it is then earthed through the alternator spade connector. When the engine is running and the alternator is working that same spade connector switches to 12v and therefore the light is no longer earthed and goes out. However, what I didn't know is that the 12v supplied to the alternator also provides an initial magnetic charge to energize rotating field coil.

Back when I was testing the oil pressure light and alternator charge light the engine wasn't running too well. So I focused on getting the engine started and then connected up the test light to see if a) the oil pressure light was out - check! and b) charge light was out. But of course it didn't go out because I connected my test light AFTER the engine was started. Doh!! So I wired it all up this morning, ignition on, light on, engine started, light off - simple.