My Denso alternator has the B (to battery) post, and just the two (L & IG) spade terminals.

With B connected to battery +, IG fed 12v from the ignition, and L fed with 12v from the ignition via the bulb I get 0.3V out of the L spade terminal when the ignition is switched on so the bulb doesn't come on. When the engine is started nothing changes?

[Edited on 22/5/08 by John.Taylor]

12v to extinguish the light on the dash when then engine is running. With engine stationary the lamp has 12v to it from the battery and the L terminal earths the lamp thus lighting it to inform you that the alternator is not charging the battery. When you start the engine then you get 12v+ to balance the supply to the lamp, 12v both sides = light out.

^ yip

I'm really not getting this alternator wiring.

I have connected both the IG and L spade terminals with 12v feeds off the ignition that come live when the key is turned, but put a lamp in line with the L feed?

When I turn the ignition on, but don't start the car, I get 12v to both the IG and L spade but the lamp (which works) doesn't come on. It appears to me that the L spade isn't earthing?

Could this be true and what does it mean?


[Edited on 22/5/08 by John.Taylor]

Here's the circuit. Been posted before.

[Edited on 23/5/08 by Dusty]
Rescued attachment Denso.JPG

Take the wire that goes to the L connector off the alternator and touch it to the engine metal ( stick a spare male spade into it to act as a probe ) With ignition on, lamp should light. If not you have a high resistance - poor connection perhaps - in the feed to the lamp.

If it lights in above, touch the L wire to the alternator body. If it lights the alternator is faulty and as you say the L connector is not presenting an earth. If it doesn't light the alternator body is not earthing to the engine block and you have made your alternator mounts out of rubber