365bb alternator help

Hi guys

I have been having problems with flat batteries. After charging overnight, voltage at the battery read 12.5v. I then started the car and voltage read 13.7 at idle. Increasing revs to 3000rpm made no differnce to voltage reading. Turned on all the lights and voltage dropped to 10.0v and car started running rough. Unsure whether I'm dealing with a regulator or alternator problem. By the way the car ammeter does not move at all from zero regardless of whether car is on and running or at starting. I read a previous thread from David Feinberg which made reference to the alternator warning light causing problems if the bulb is blown. An alternator warning light does not come on at all in my car, and I'm not sure whether that is the problem or if the car was never fitted with one (#17915 - which I believe runs the Marelli type alternators and not Bosch like the older cars)

I would be grateful for any advice

Thanks

Greg

Greg,

Although you have an earlier car than mine, functionally the charging systems work the same. When the key is first turned on, the "Battery" light must be lit to provide excitation current to the alternator...The wiring diagram I have shows that (all?) cars have a warning light, but who really knows for sure. What's odd is your statement that you do have 13+ volts across the battery with the car running. That would tend to say that your system is indeed charging...

Secondly, if you're charging you battery overnight...and only have 12.5 volts, there's a very high probability that you have a bad battery.

If you BB is still using the Digiplex/Dinoplex ignition system, the car will run very poorly if the battery voltage is low.

Although the ammeters in these cars are heavily dampened, they should move positive (charging) when the car is first started.

First step: Have the battery load tested. I suspect that there's an internal problem with your battery. If that's the case, replace the battery and re-measure the voltage again under load.

I have run into bad engine to chassis grounds (left side of transaxle near the front of the engine) or at the battery itself (grounds to chassis under the battery box).

If after all above is done/check, the alternator is fairly simple to remove from underneath....and with the possible exception of mounting shims, the Bosch alternator should be a bolt-in. Both the Marelli and Bosch alternators were used in Fiat 124s of that era, so getting it rebuilt, and/or finding parts should be non-issue.


Regards,
David

Thanks David. I'm beginning to wonder if someone in the past had done some "creative wiriing" as a have never seen a battery light turn on in the past five years I've had the car and I don't really recall ever seeing the ammeter needle move. I'll check it out as you suggest and report back. thanks again

The plot thickens.... I had a look at the instrument panel and there is no battery warning light. At the bottom of the tacho, immediately to the left of the midline there is a warning light (yellow) with no symbol. There is a bulb connected to it which looked ok and as far as I can remember has never lit. My owner manual designates this light as a "spare" which I assume means it has no function, but curiously there is a bulb and wiriing attached. The ammeter probably does work as when I tried to fire her up the needle moved ever so slightly to the left. Had a look at the alternator as well it is a Bosch type with no obvious separate regulator(so looks as though this had been replaced in the past. As David pointed out, seeing as though the voltage across the battery did increase with car running, I'm hoping the alternator is Ok. Won't have time to load test the battery till next weekend, but will report back what I find. I love this site! JRV best wishes

Greg,

No surprise on the alternator swap...Parts are far easier to find for the Bosch unit anyhow.
I'll check my car later for the exact location of the charge warning light, but if my memory serves me correctly, the lamp is "Yellow" and not labeled.

Back to you later...


Regards,
David

ok. Think i'm sorted now. New battery. Voltage readings as follows:

car off 12.2v
idle 13.5v
3500rpm 13.7v
all lights on/3500rpm 13.7v

So I would assume alternator is ok and problem was a bad battery

I'd say so...lots of battery troubles lately..proves the old adage "If ya' can't crank it.....yank it!" LOL!

That looks like good readings to me.........