Need help with charging system light?

Ross it is starting to sound like you may have an open circuit from the alt to the light. You may need to ring out the wire from the back of the alt. to the light. Also when was the last time this car was run. Is the alt clean and free of any oil or dirt. With the key on doese all of the other elect things work? Also check the fuse block and make sure with the key on that you get the correct voltage at the fuses. Also it might be a quick check to hook up a volt meter to the B+ post on the alt and see if you get 13.6V at 1000 rpm. If not you would need to pull the alt and rebuild it. If you do that make sure they build it to the 85A upgrade. Good luck

 

Ross

How did you measure the 11.94 volts? across the connector to the bulb or by taking the meter - to a seperate earth point on the car. Do you get the same results if you try both measurements. Are you missing the earth return from the bulb or could it have high resistance?

john

 

Ross based on what I remember the dash light needs to be lit with the key on and is fed by the sense wire off of the back of the alt. This comes from the rectifier bridge and returns back through the regulator. It will go out when the alt starts to charge. So if you have continuity on the wire I am leaning to the theory that either the rectifier bridge has a blown diode or the regulator has died. So do a little more checking and maybe even replace the bulb but my gut is telling me you will need to pull the alt and bench test it. Then rebuild it . I have just started to do a belt change and getting the alt out will be a slight PITA but only a few hr. job. Good luck.

 

HAHAHA , if you want to take a look on how to remove it just pull off the pass. side wheel , take the screws out of the fender inner liner. Look down on the lower right side and see if you can spot the alt. I used to remove / rebuild / reinstall alts on Volvo's and Corvette's and most other cars in a 1/2 too. It takes 1/2 hour to get to see the alt. HA enjoy

 

The dash light bulb has switched power, through the ignition switch, on one side...and in a non-charge mode, gets its ground through the diode tree in the alternator. To verify the wiring from the dash to the alternator, unplug the alternator, turn the key on, and ground the "D+" wire going to the alternator. This shhould turn on the dash light, hence verifying the circuit integrity. If the dash light does turn on, you know that there's an internal problem with the alternator. When an alternator is charging properly, there will be an output voltage on the D+ lead; hence the dash bulb will have 12 Volts on both sides of it...and will not light.

Some alternator circuits require the bulb circuit to be functional, as the initial excitiation current flows through the dash bulb. In any case, you'll need to verify the wiring.

Regards,
David

 

Not a lot to add after David’s excellent post which describes exactly the operation of the charging circuit an how to verify the circuit integrity before removing the alternator.

 

Dave good post

 

Thanks Steve...

I've chased more than a "few" of these charging system problems and it's far to easy to just replace parts....only to find that there's a problem in the harness, or worse...a blade connector that isn't secured in those flimsy plastic plugs! My money is with yours on a bad diode tree in the alternator, but let's first see if his harness is any good.

Regards,
David

 

Ross,

The alternator is just a plain jane Bosch unit, similar to, if not identical to, what was used on many Fiat 124 Sport Coupe. Any....and I mean any compentent alternator shop (No Dealers!!) can do this rebuild for less than $100. Some shops may have the capabilities to "upgrade" it's output. This is not a bad idea, with zero downside risk. Just tell them it's off an old Fiat....Rebuild psrts are common and plentiful for these units!

Diodes are odd little devices to measure, particulary if you are not using a high impedence meter. Rather than speculate on what I think is happening internally, once you get that bulb to illuminate, then...I'd pull the alternator and be done with your pain.

About the only thing my BB has over the 308, in terms of ease of service, is that I can have the alternator out in 30 minutes...

Take care,
David

 

Ross if you get it rebuilt tell them you want to boost it up to as much as possible. My 77 was a 65A OEM and I had my rebuilt (by an auto elect. place) to an 85A output. It coast me $110 around 5 years ago. I had a cam cover leak and the alt. got bathed in oil. I also asked them to seal the armature. The thing you want to watch out for is the pulley. This is special and you want to make sure that they don't loose it.

 

Sorry Ross....It's not you. It's just nothing ever seems to comes out, as it appears, with just a "few bolts" on a Ferrari. But, yes...pull, the wheel, the inner fender and disconnect the battery. With a few skinned knuckles and a few more well-choosen Italian swear words, she'll be out.

Regards,
David

 

You might not want to put too much stock in your "resistance" measurements: ohmmeters are designed to work on circuits with no other power source except the meter itself. An ohmmeter applies its own voltage and measures current. Any other power in the circuit will throw the reading off.

Diodes are designed to pass current in one direction only, so they will also throw off a "resistance" measurement. A 1.5v drop across a forward biased silicon diode is pretty normal. Unless you know the details of the regulator circuit, it's hard to interpret what an "ohmmeter" reading might mean. (The regulator was a separate component in '70s Alfas. Those were fun to diagnose.)

But, as said above, since the regulator is built into the alternator, these days, if the sense/starting circuit (through the lamp) is good all the way to the alternator, then there's not much point to rebuilding just part of an alternator.

 

Ross when you look under the car and see the alt. you will notice it has a heat shield bolted on the back. This can be removed and the regulator replaced but it is a pain in the butt to do it. And as DGS mentioned it isn't worth just changing the reg. without doing a bench test and or an upgrade. So it sounds like you are not getting the desired results and you'll need to bite the big one and pull the alt. So welcome to our world and just look forward to this experience as fun. I think we all know the Italian swear words (in the back of the OM) so you'll now be able to expand your mind. HAHAHAHA Good luck from the bloody knuckles gang.

 

OK sounds like you are doing good . Some folks don't find the alt on the 1st try HAHAHAHAHA. Yep you need to remove the shield and Iam trying to remember but I think it is 3 bolts that hold it on. Once that is done then you can check out the electronics. And yes you need to drain some water and take the water pipe off at the top of the water pump. Now here is where you have some more fun. There is a petcock on the back of the block just below the header. If you open this you can drain off a few qts of water but this is a mess and you will get an uncontroled amout of water on the floor. Now if you have not changed the antifreeze in a while let us know and we'll give you the method that a lot of us use to drain the system. So see if the alt puts out and if you need to remove it then we'll talk about the cooling system. HAHAHAHA we are all loving this thread because we have been there and are still pissed HAHAHAHAHA. I hope you feel better. I usually don't put any ice in my scotch when I'm sick.

 

Ross,
Aren't you done....yet?