Lotus Elan

ignition warning light - denso alternator

PostPost by: lightwait26 » Sat Sep 19, 2020 11:53 pm

About 2 years ago, I fitted a Denso alternator (RD/ Gustafson). Simple install, new wiring. Everything worked out fine, big improvement.

I drove the car last week, and noticed that the ignition warning light was not coming on at any time, even with just the key in the on position. I have a rudimentary volt meter, and hooked that to the battery. Voltage rose with rpm increase, so I deemed the alternator to be working. I did a check of alternator connections, and also the connections to the terminal box which replaced the voltage regulator, also looked fine.

From reading past threads on here, I saw that the alternator would send a ground signal to the light, causing it to light until the alternator begins charging, whereupon the ground signal would go away, causing it to go out.

Next step was to remove the warning light from the tach, both wires were connected. With the key turned off and a test light used, both sides of the bulb showed ground. With the key turned on, or the motor running, power is shown on both sides of the bulb, and touching an external ground to the socket lit the bulb.

I am kind of puzzled as to what to do next, any input would be great.
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PostPost by: mbell » Sun Sep 20, 2020 2:48 pm

To take a step back, there are three basic causes for the light not working:
1) no 12v supply to the bulb from the ignition switch
2) a bulb issue
3) no ground connection when ignition on but engine not running/charging.

Possible causes for each I can think of are:
1) wiring issue or issue with ignition switch (probably noticed for other reasons)
2) blown or incorrectly rated bulb
3) a wiring issue or fault with alternator not providing ground connection

I think your issue is probably 3) so you need to check the alternator side of the bulb for ground connection with ignition on but engine not running. (Note you need to check for continuity between the wire and another ground point not for 0v)
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PostPost by: gjz30075 » Sun Sep 20, 2020 5:55 pm

Same issue a fews years ago. Had the RD Nippondenso alternator in for about 11 years. Light goes on
one day and of course not charging. Had it rebuilt, same problem. I take it back to the rebuilder and shows
me on his test machine that it works. I take it to several 'big box' auto parts stores for testing and all
testing shows good. Just won't work in the car.

I changed the bulb to different wattages; still fails. I ran a separate charging circuit, outside of the car's
wiring. Still fails, ie, the light remains on.

I bought Nippondenso alternators of the same ilk from several auto parts stores and none of them would
put out the light.

A Hitachi alternator solved the problem.

I'm guessing that the current rebuild process is putting in a regulator of some sort that doesn't like our low
wattage bulbs.
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PostPost by: lightwait26 » Sun Sep 20, 2020 7:08 pm

mbell wrote:

I think your issue is probably 3) so you need to check the alternator side of the bulb for ground connection with ignition on but engine not running. (Note you need to check for continuity between the wire and another ground point not for 0v)



Pretty accurate assessment. It seemed like the alternator was not providing the correct ground signal to light the bulb, so I went back and rechecked the wiring diagram and wiring.

And then......,<red face mode on> I realized that I had one of the spade terminals on the wrong one of the 3 terminals on the alternator....<red face mode off> It truly is amazing how well an electrical item performs when connected correctly. :oops: :oops:

Anyways, thanks to those who responded. If nothing else, I learned a lot about charging system functions. Thanks!
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PostPost by: Esprit2 » Sun Sep 20, 2020 11:30 pm

The "ignition warning light" really doesn't have anything to do with the ignition. The alternator's field coils (stator) doesn't have enough residual magnetism to start generating current upon first start. So a wire runs from the ignition switch, through the idiot light, through the alternator's coils and to ground. Switch on, and there's enough current passing through the alternator to get it kick-started.

Once it starts generating current, power is tapped of to self-energize the coils. After that, full system voltage exists on both sides of the idiot light (from the switch, and from the alternator), the voltage is balanced so no current flows, and the idiot light goes out.

If your alternator starts producing current immediately after the engine is started, then it must be getting the priming current. But normally, when an incandescent lamp burns out, the circuit is 'broken'... goes 'open'. So how is it that your idiot light is off, but your alternator works? I don't have an answer. Not unless that particular 'modern' alternator has sufficient residual magnetism to self prime. Just a guess.

*~*~*~*
In some cars, the priming circuit also runs through an oil pressure switch. Not the gauge sender, but an on-off switch. Oil pressure holds the switch open so the idiot light goes off. Any time the oil pressure drops below some minimum, the switch makes contact, and the idiot light turns on. Same light, but two circuits feeding it. I'm a Europa guy, and I don't know if the Elan uses that feature. It's just something else to be aware of when you're poking at wires/ tracing schematics.

Good luck,
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PostPost by: Andy8421 » Mon Sep 21, 2020 5:45 am

Esprit2 wrote:The alternator's field coils (stator) doesn't have enough residual magnetism to start generating current upon first start.

On an alternator, the field winding is the rotor, not the stator.

The Lucas xxACR range generally had enough residual magnetism to pick itself up by its bootstraps without the ignition warning light if you gave the throttle a decent blip. I am not sure if the same is true of the Denso alternator.

Reviewing the symptoms, my guess would be that either the connection between the bulb and the alternator has failed somewhere, or that the voltage regulator has failed in some interesting way. Have you checked the circuit from the bulb to the alternator for continuity?

I would note that if 'touching an external ground to the socket' was done with the engine running and the bulb holder in circuit, there is a chance you have blown part of the voltage control electronics in the alternator.

Good luck.
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