Generator Light ?

My GT4 use to have the gen light dim and was only noticeable at night and especially when I would have the headlights on as well as the brakes.I think its normal for early 308's.When my alternator failed,the gen light came on bright.

 

Sledge 4.2, I wouldn't be too concerned about the alternator light coming on a little at idle (so long as it goes out promptly when the rpm increases) - that's pretty common for many Italian cars.

If you think you have a weak battery then best to replace it with a good quality replacement. 308s have a weak enough electrical system as it is, you don't need a weak/failing battery making things worse. If the voltage gets too low you can end up with all kinds of electrical gremlins including poor engine performance, particularly with the CIS and other/later Bosch-based systems. A good battery is not that expensive in the big picture.

 

Sometimes the light will glow weakly when a diode in the alternator is going south. You will probably need an alternator overhaul soon, maybe just the regulator.

 

If the car ran well after a full battery charge, then it is probably the alternator failing to keep the bat charged.
The battery could very well also be bad.
Did you find a date code on it? If it is anywhere close to its rated life, it is probably toast.
I just replaced the battery with a 72 month unit from napa, as well as the alt, (Bosch rebuilt from a 80-81 Fiat 124). You will need to reuse the back shield, pulley assembly and buy a new mountng bolt because the fiat housing does not have a big hole in it for the ferrari rubber mount bolt. No worries works just fine.

If the battery doesn't fix the problem, then you will need to do the alt. It is such a pain to get in and out, i would go for a full rebuilt unit or have yours rebuilt and tested. (Not all rebuilt alts get tested).

hth,
chris

 

Sledge,

First off its an alternator not a generator. On my GT4 which is probably the same set up as yours my light comes on full at startup but once the rpm's come up it goes off. I hardly ever drive at night so I cant comment on the dim but I bought a new alternator from *** a couple of years ago. I took my old one to a shop to haave it fixed the guy was such a jerk and there is only one place in town that does them i just bought a new unit it was not much i think 300$/ I have been having problems putting aa stereo in my car so i bought on of these it works real good but unless adjusted interferes with my hand brake lever.

http://www.amazon.com/gp/product/B000EVWDU0/ref=ox_ya_oh_product

I would highly suggest one for all your cars. I think pilots use them....

Rob
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Just to be clear and precise, if the alt light comes on occasionally at idle but goes out promptly when the engine rpm rises above 800rpm or so then you don't necessarily have a bad alternator. The output can be so low at really low rpm as to trigger the light without having a critical problem.

Also, to be clear, it's the thresh hold voltage you want to focus upon - if the battery is bad (sound like it isn't) then that can contribute to low voltage, however, it's the alternator that controls voltage (via the voltage regulator) not the battery.

My guess is that your carbs need to be cleaned and synchronized (perhaps even rebuilt). Welcome to the world of weber tuning.

 

Inexpensive design is for lamp to go out when alternator voltage exceeds the battery voltage (cheaper than a voltmeter gauge and less idiot-prone). Alternators are designed to function reliably in the rpm range of passenger cars. Ferraris have a higher top end rpm requiring a modified pulley ratio to accommodate this. Result is higher idle is needed for low end minimum voltage to turn off the light indicating satisfactory charging conditions. Start current expended droops the battery slightly and after a minute or so, an idle of 1k rpm will extinguish the light whereas it's oft 700 rpm or so in a passenger car. Depending on the diode pack, some indicator lights will go dim and some off and still be normal.

 

My alternator light was on dimly on every Italian car I ever owned, but only noticeable at night. It's on dimly in my GT4 but again only visible at night and is clearly charging ok as I've never had to touch the battery in three years driving and perhaps used only once a week - but I guess you should get it checked out. Most auto shops have an on-load test device.

I've not pulled mine off, but it looks the same as a 70's Fiat one - can anyone confirm ? and is there a better modern replacement (like the lightweight starters).

Lee

'77 GT4

 

I bought a 1980 Fiat Spider alt and it was exactly the same as the one I pulled out of my GT4, just had to swap the pulley over. The K-Jet cars had a different alternator, more output to deal with the increased electrical load of the injection system, so I think this is valid for all carb 308's. With the new alt the light will not go off until the engine is revved over 1500 rpm, then it goes completely out and stays out, even at night with all the lights on. (And I have K-Jet, so I have the increased electrical load, still ok at night)

 

Who knows???

It's an indicator light, off an over/under voltage relay....so I have observed the behavior in my three cars...

Dim after start up does indeed indicate a component failing in the alternator, the diodes or the regulator (which is built in) so you may be on the way for a rebuild ($75 - $125 around here).

OTOH if it goes out above an idle it may be okay for a long time....I routinely note mine at night (when lights A/C and the stereo cranking on current draw) sometimes will blink on off on off in time with the turn signal indicators! It's a standard 65Amp unit which SHOULD be plenety for the dinky electrical loads of our cars......

There's an uprated one to go larger but then you'd have to evaluate all the wiring to avoid trouble. I just rebuild mine "as is" and roll on down the road.

You may want to be sure your dinky lil' 7mm belt driving the unit is tight and not slipping.

Now when the alternator fails and puts 20V on your headlights and blows them up....well, you'll never see it coming! LOL!

 

Well sure, any time the alternator drop below 13V ouput, our coils are fired off the battery voltage ONLY (12V on a GOOD day), in my experience (throwing or burning the drive belt off) you only have a few blocks to roll, with engine power falling, the whole time.

 

my alternator has done the same thing forever now. I measured output just as you did and it yielded numbers that are consistent with a good alternator. Dont worry about it unless the charging numbers go south.

 

Check the dwell on your points. Could be a simple enough issue.