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Wimby alternator ?

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donandmax

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Subject: 79 MG Midget alternator.
Problem (?) Someone may have addressed this issue before, Don't know if it ever got answered. When I turn on my headlights and heater blower motor My red idiot light glows ever so faintly. When I add wipers and radio it gets a little brighter. I changed the alternator from Lucas to Bosch they have the same wattage (37) Same problem. I then changed to the Ford Fiesta (55 amp) alternator. Same problem. Anybody have any idea of whats going on here ?My battery never goes dead every thing seems normal except that faint glow when I add anything on except the headlights. Surely 55 amps should be enough to keep this light completely out. Your input will be greatly appreciated.. And Thank you
Don
 
Hi, Don -

Rule Number 1 (At least for me):

Check your ground connections. I've found they are the usual suspects. Be sure you have a VERY good ground from the engine to the body/chassis.

Mickey
 
Yeah, this really sounds like a bad contact or ground problem to me. I can't imagine anything else, other than an incorrect hookup. You might make some voltage measurements with an analog voltmeter (don't use a digital one--they're upset by the electrical noise in any automotive electrical system). Start by seeing if there is voltage between the engine block and the body when the problem is occurring; if so, there's definitely an inadequate ground between the two. Also, check the system voltage, generator output voltage, and just poke around to see if everything makes sense.

This is worth some trouble to fix it--the generator output could be low because of the bad connection, and then you might be undercharging or maybe even overcharging the battery. Either one can shorten the battery's life.
 
This might sound like a dumb statement, but double check the tightness of the alternator belt. They have to be tighter than you think. I went through this on my wife's Ford Festiva. What was happening was that with a light load the belt did not slip but at a higher load the belt would slip. It nearly drove me crazy until one day I had just started up the car and turned on everything electrical I could think of and then checked a few things and turned the car off. I touched the alternator pulley and it burned my hand. Ah ha! Friction, tightened the belt and the problem was solved.
 
Well guys this is really a perplexing problem. Ive checked grounds, belt tightness. Cleaned everything up and no luck. If I turn my lights on the light stays out. If I turn them off and turn on either the blower motor or windshield wipers I get that faint glow (yes even with the lights off) Iam about at a loss here. Why should the wipers and/or the blower motor turned on cause a faint light to come on. Ive checked the obvious. Looks to me like someone else may have had the same problem because the blower motor looks like it has been replaced. I guess they might have just given up.What about the fuse box could that cause any problems like this. I've had this car now for about 6 years and it has always acted this way so it's been going on for some time. I almost never drive it at night and use the blower occasionally in the winter. So never have taken it on a trip where I had to use the blower or wipers. Battery therefore stays charged.
Thanks
Don
 
Clean off the green. Both is fusebox and all bullet connectors. SAndpaper/emery cloth for the bullet ends and a small drill bit for the femal double end connectors. Bet it solves your problem.
 
Kim, I did some voltage checks with my meter ywsterday. Heres what I got. Engine off 14.5 volts. Engine on and idling 15.5 volts.
Engine idling with all electrics on. 14.6 volts. Either my vtvm is off or wrong but the engine and electrics off figure shows a static charge of almost 15 v. Is that normal on a 12 v battery ?
Don
 
15.5V is way too high, and the output of a modern alternator should be rock stable as you change loads. It should hold the battery around 14.5V.

I suspect this is caused by the alternator's regulator failing to sense the voltage correctly, which is why I thought (and still think) it might be a bad or incorrect connection somewhere. Some do this internally, others have a separate "sense" terminal which is tied to the battery. In others, the voltage is simply sensed inside the alternator. If the regulator senses a voltage that is too low, it will increase the alternator output beyond what it should be.

Check the voltage at the alternator's D+ terminal if the voltage is internally sensed. That's usually the sense point and it's also the connection for the ignition lamp. I'll bet it's low. It pretty much has to be, if the lamp is lighting. Is anything other than the light connected to this point? There shouldn't be.

Also, any chance that the sense terminal (if external) is somehow shorted to ground or not connected?

Check the voltage between the alternator body and car body. If you see any voltage, there's some extra resistance in the connection between the block and body, which might be affecting this. In any case, it's a problem.
 
Steve, no voltage between alternator and body. Alternator and regulator (built in) are new (rebuilt) Ford fiesta type. Everything on alternator is "plug & play"
It's doing the same thing as the Bosch alternator it replaced. which was also nearly new.. Things have improved since I cleaned the green off of the bullet connectors. And that seemed the reason for the improvement. I can now turn on lights and blower without the faint glow. However when I add wipers it glows slightly. Havent had a chance to clean off the contacts on the fuse holder yet, However they look pretty good.
Thanks
Don
 
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