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Red Light on Dash

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jcatnite

jcatnite

Jedi Knight
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All,
This morning after filling my 76 Midget with fuel, I started it up and headed down the road. I immediately noticed the red light on the dash above the high beam indicator glowing bright red. Usually it is bright red when I start it and it dims down to barely perceptable when I rev the engine. Anyway, I know this light is related to the charging system in some way but don't know if it is triggered off of voltage or current output. Does anyone know for sure what causes this light to glow? I know the PO has recently replaced the Voltage Regulator inside the altenator and had put a new battery on it. Just wondering where I should start checking first.
Thanks,
JC
 
Hi JC, the light means that the alternator isn't making enough output, either because the belt broke or the alternator had some failure inside. My alternator was dead when I got my car, but I got the replacement from Autozone. It was cheaper than one from Moss and had a lifetime warranty on it. The quick way to ID the alternator as the culprit is to unplug the harness from the alternator, turn the key on, and if the light is off, it's the alternator.
 
To be more specific on what triggers the light, there is a diode trio in the alternator that is separate from the high current rectifiers that supply current for the rest of the electrical system. The diode trio supplies voltage to the regulator, and to one side of the warning light. The other side of the warning light is connected to the battery. If you really want to troubleshoot the alternator, the usual suspects are the regulator, the slip ring brushes, the diode trio, or the rectifiers. Oh, and you might want to disconnect the battery until you've done some troubleshooting. If the rectifiers or the diode trio are at fault, they could kill your battery even when the ignition is off. Hope this helps!
 
Sparkydave, can you elaborate a little on the diode trio? I know it supplies a signal to the regulator but why do these fail instead of the diodes in rectifier circuit?

I have not studied Lucas alternators by themselves, but have worked with alternators in general when necessary. It is my understanding that the charge indicator light is (as Sparkydave described) connected to the battery (through the ignition switch) on one end. The other end of the charge indicator lamp is connected to the field coils of the alternator on the other end. When the ignition key is on and the engine off (not running) the alternator coils are charged up by current passing through the warning light. Once the alternator gets up to speed and starts making electricity, its internal regulator provides alternator output to the connection point for the indicator lamp to "self-energize" the coils. At this point both sides of the charge lamp are at the same potential so the light goes out. (Correct me if I'm wrong Sparkydave).

Be careful if you are testing the alternator in situ. Do not disconnect the battery while the engine is running. Only make/break such connections with the engine and ignition off.

BTW, you can take the alternator off the car and into places like AutoZone, Advance, etc. and they will bench test it for free.
 
Hi Doug, you are correct about the connection of the indicator light, it is connected to one side of the field winding so the field gets a little bit of excitation current so the alternator can self excite. Once the alternator is spinning, the diode trio is separate from the rectifier stack and only provides the field excitation current. The output of the diode trio is connected to the positive side of the field winding, where the indicator light is connected. Once this voltage is equal to the battery voltage the light goes out. The regulator output is connected to the negative side of the field, and by controlling how much current flows through the field it controls the alternator's output. Note to JC: I remembered that if you do get a new alternator, you might need to save the pulley from the old one. The one I got from Autozone came without a pulley, so they had to swap it at the store.
 
Also, you may want to look at what type of pulley. When I got a new alternator the fan on the pulley was completely different. (much much bigger dia.) When I got it home it interfered with the fan belt, something the old fan and pulley would not have done.
 
Wow, thanks guys. I never dreamed that this discussion would get so deep. I feel like I'm in Basic Electrical Engineering class again...lol. Guess I will be doing a little electrical work this weekend. Just realized that it is raining here...silly me didn't put the top back up this morning so Rusty (my midget) is sitting out in the parking lot getting all wet inside...
JC
 
Well, Rusty got me home. Seemed as though there was no shortage of power for the ride. I did notice that the light would dim slightly just above 1K rpm but would go right back to bright red while waiting at a light. I checked out Autozone and Advance Auto to see how much bank I was going to have to shell out and found that the alternators they have are 36A??? Is that all the little car has now? I have no aspirations of 15 inch subs and plasma tvs someday but 36 amps seems a little weak. Maybe that is enough just seems small to me...
JC
 
[ QUOTE ]
the alternators they have are 36A??? Is that all the little car has now? I have no aspirations of 15 inch subs and plasma tvs someday but 36 amps seems a little weak. Maybe that is enough just seems small to me...JC

[/ QUOTE ]
36 amps is about 500 watts. A lot better than the 22 amps on some of the older cars. How much do you need?
D
 
Hello jcatnight,

before delving into the electronics, did you verify the drive belt? This is the most common cause of poor output.

Alec
 
Hi JC, the original was also 36 amps. I was a little surprised too, but when the most powerful accessories on the car are the 60-watt headlights, that's plenty. Supposedly there is a way to adapt a more powerful (and reliable) AC-Delco alternator, but I see it as "if it ain't broke, don't fix it".
 
When Dave Russell says 36 Amps is more than enough then I'm on board. I have no need for more power and sure don't want to go through the gyrations of trying to adapt an AC Delco altenator in the car.

piman - I did check the belt and it is tight. The I haven't pulled the connector from the back of the alternator yet. Should be able to do that tonight. I also suspect the connections so I will clean them up and see if that helps.

Thanks for all the help gentlemen!
JC
 
If all you are running are the standard lights and basic radio 36 amps are more than enough. You may notice the turn signals blinking slower at stop lights, especially at night.

I converted my '78 to a Delco for three reasons. One,I have installed halogen headlights and tail light bulbs and wanted the extra power.

Second, cost. I was able to get the Delco (rebuilt unit) for about $45, including the various fittings I would need vs. about $90 for the Lucas.

Lastly, availability. If I need to replace the unit again, it is readily available anywhere.

Other people have done a Bosch conversion saying it is easier.

Since I did it once, it would take me about 30 minutes to do a conversion on another 1500.
 
OK just a quick update. I finally managed to get the plug out of the back of the alternator...was afraid I was going to break that brittle plastic and with the key on the light is off. According to SparkyDave that means the alternator is suspect. Guess I will pull it off in the morning and take it up to the parts store to have it tested.
Mike - which Delco alternator did you use? Probably not entertaining the idea right now but might come in handy in the future.
JC
 
If you were a Doctor; you would just put black tape over the light (like Asprin for headaches). Cure the problem by replacing the alternator if it tests bad or weak. But the reason I jumped in here is... several of the guys have links to using a Delco alternator instead of a Lucas. They last longer and operate the system properly. I have one in a 79 MGB and also in a 76 Midget. Lucas is where you want to be if you are working toward a perfect restoration but if you want to drive it... switch to something else. In the arcives of this site are links and discussions on non-Lucas exchanges. Look at them and have some fun driving this summer.
 
I looked at the Delco swap threads pretty extensively. I was pretty sold on doing one until I saw how big the delco alternators are. Not sure if I want to go there right now. I was going to pull the alternator this afternoon since I had to run to town anyway. Well after about 30 minutes I realized that I couldn't pull the alternator without pulling the radiator as well and got frustrated. Put the tools up, put the bolts and nuts that I had out already in a bag, and shut the hood. I'll try again when I have a little more time.
JC
 
Ask Nial (Aeronca) about his mitsubishi alternatore job. If you check his profile, I'd imagine that you'll see it somewhere on his webpage, as that's where I remember seeing it. It seems to me that he said it was significantly smaller and had either an intermediate or similar output when compared to the Delco unit.

Matt
 
I switched to an alternator when I went from pos. to neg. ground. I used a Nissan pick-up alternator. It's small,strong and has the right pully spacing etc. Really easy conversion.
 
Today I bought the bullet and performed the delco alternator conversion. It took me a while to make all the modificatons and the alternator looks like a 55 gallon drum hanging off the engine but boy what power. The midget hasn't been moved in a month(been out of town and working 7 days a week) and she fired right up on the first try. I think it might even idle a little better than before...lol. Seriously it does seem to be running a bit better. It took me about 3 hours to do the job (including 1 trip to the hardware store). Only time will tell if the belt wears even or if my calculations were flawed. Without access to anything more than a hacksaw and flat file for metal working, I might have left a little too much material on the lower mounting bracket. It's raining now so I can't drive it but I'm itching to get it back on the road.
JC
 
I did the same with the Delco. Be careful of the connections -- having charging difficulties I'm still working through (either too much or too little).

Also -- use super hardened bolts to secure the alt to your homemade bracket -- I snapped my "plain jane" ones. All items from Home Depot -- just an oversight on my part, luckily I was close to home.

Geo Zeck
 
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