Alternator Wiring

[SteinOnkel]

Hey guys,

I tore off a wire on the alternator the other day. It was purple, so I soldered it to the other purple end on the engine bay harness. Now the alternator light is constantly on. Anybody got a wiring diagram?

Thanks
Manuel

[TX82FIAT]

I have to ask... I'm sure you did... Did you disconnect the battery wire before soldering? A solder connection should have the best conductance and the alternator light works off resistance. It is possible the circuit could have been damaged when soldering. Maybe, if the wire was broken/torn and not cut, you have bad conductance in another area of the wire where it was stretched before or after the area where the wire tore/broke. Conductance test on wire?

[SteinOnkel]

Hmmm that is worth looking into. Does the wire go from the alternator, to the bulb and then to the battery or...?

Alternator isn't reaaaaally charging the battery either. 12.3 Volts at rest, 12.3 volts after 30 minutes of driving (second measurement while car was running).

[rridge]

The alternators used in 124's are not self exciting. They need an initial source of power to begin producing. That source comes from the battery via the alternator light bulb and on to the alternator. When the bulb fails or when the wire between light and alternator is broken, the alternator goes off line.

[TX82FIAT]

As I understand it, rridge is correct. Seems silly that a light bulb out could be the source of alternator and subsequent battery issues. But, I had the same issue on a spider years ago from a bulb being out. Your light is on making it likely to be a wire or the alternator itself. Since you broke the wire, I'd start there.

[SteinOnkel]

Hmm it's very strange. The wire is fixed, the bulb constantly on. But I drove the car 150 miles on Saturday without any issues. Then I measured the battery yesterday after sitting all night and it has 12.7volts. It wouldn't be able to do that if the alternator wasn't charging.

What am I missing here? The alternator only has the big honkin' wire to the starter and the small exciter wire for the bulb, correct?

[TX82FIAT]

Is it a new battery? 12.7 volts the next day seems like a new fully changed battery. Is the light still "constantly" on or is it intermittent at some RPM? Clearly charging if you moved the measurement from 12.3 to 12.7 volts. Perhaps the previously broke wire now fixed gave a false positive to circle around the wire as a likely issue. Maybe an internal issue with voltage regulation or some other component of the alternator like the brushes. Do you have one of those digital cigarette lighter voltage meters for $3. Plug that in and see what the car does at various RPM's. I have seen where an alternator that cannot regulate voltage overcharges a battery causing issues. All these systems need top be within a range for the light to not come on.

[spider2081]

there is a 1978 wire diagram in the Mirafiori.com library. I think its for a Bosch alternator. The battery warning light wire is Violet/black. Hopefully the wires you connected together were both violet with a black trace on them.

Generators usually have a permanent magnet that needs to be correct polarization for the generator to function. The magnetic field is required for the generator to produce an output when it turns. Alternators do not have permanent magnets I believe this is because the magnet would become too large for higher current ratings. Alternators use an electromagnet, meaning current must be flowing through its winding's in order to produce a magnetic field. This current flow is said to excite the alternator. For many alternators a simple way to accomplish this is to use the battery warning light.

If you connected the wire properly pulling its connector out of the alternator with the key on and the engine not running will cause the battery warning light to go out. It that happens and your battery warning light does not go out with the engine running the voltage regulator may be faulty.
Can you post a photo of your alternator??

[SteinOnkel]

Hey guys,

I made a quick video:

https://youtu.be/auabxI8rMfc

After the video, I decided to plug the light back in and start the car. Light stayed on constantly and the voltage at the battery dropped to 12.4 No amount of revs would bring it back up either. Totally lost in this regard now.

Also to the carburetor issue so far I have:

- removed and plugged any emissions malarky
- cleaned the carb with copious amounts of carb cleaner
- blew every passage out with compressed air
- installed a rebuild kit
- gone to electronic ignition, set at 10* TDC at idle (but this makes no difference)
- checked for vacuum leaks with various methods
- checked valve play

And still the damn thing drips fuel from the main venturi onto the throttle blade at idle and just off idle. What gives?

Cheers
Steiny

[SteinOnkel]

Hey guys,

I made a quick video:

https://youtu.be/auabxI8rMfc

After the video, I decided to plug the light back in and start the car. Light stayed on constantly and the voltage at the battery dropped to 12.4 No amount of revs would bring it back up either. Totally lost in this regard now.

Also to the carburetor issue so far I have:

- removed and plugged any emissions malarky
- cleaned the carb with copious amounts of carb cleaner
- blew every passage out with compressed air
- installed a rebuild kit
- gone to electronic ignition, set at 10* TDC at idle (but this makes no difference)
- checked for vacuum leaks with various methods
- checked valve play

And still the damn thing drips fuel from the main venturi onto the throttle blade at idle and just off idle. What gives?

Cheers
Steiny

[DieselSpider]

It may be time to take the alternator to a local O'Reilly or Advance Auto and get a free alternator test to verify you didn't blow a diode when you were patching things up.

From the video the alternator is getting excited when you unplug the light (purple/black wire) since in the video your are getting 13.8 volts when its unplugged so I would put the meter on the purple/black wire when its disconnected to see if your getting a voltage reading between it and the ground or a continuity reading indicating a short. If its reading a short circuit then leave it unplugged until you track down the source of the short circuit. Does the purple/black wire get hot when its connected to the alternator? It should even if there is a partial short circuit.

[Odoyle]

As Dieselspider said, check the B/V wire for 12V when the key is in the #2 position before starting. It connects to a male spade below the main alternator stud. Few other things to consider are 1. making sure the choke is properly adjusted, it should be fulled closed when trying to start the engine cold and open up and stay open as the thermostatic spring expands from the temp of the coolant getting hot. 2. Idle cut-off solenoid on the carb will close the idle jet passage unless it has 12V, which is coming from a thermostatic switch underneath the intake manifold. 3.Having the fast-idle mechanism connected does have some legitimate benefits, it will increase the idle speed to help prevent the car from stalling, can confirm that it does make the car easier to drive compared to my 83. Do you have a shop manual?

[spider2081]

Its my understanding an alternator requires excitation to begin its operation. Once the alternator has an output the voltage regulator controls the alternator.

I would first test your battery warning light circuit. When the engine is "off" and the ignition switch is "on" the battery warning light should be lit. Once t he engine starts it should not be lit.
To test the battery warning lite circuit:
Remove the black/violet wire from the alternators terminal. With the ignition key "on" and the wire not touching anything the light should not be lit. Grounding the wire should light the battery warning light while the wire is grounded. This is how to test the light circuit.
Using an ohm meter to check the black/violet wire could be very misleading. An ohm meter will find many sneak paths through the lighting circuits. All the light bulb filaments are in parallel so the meter could indicate a short when there is none.

Many solder irons have a "grounded" tip. Soldering the violet/black wire without disconnecting the battery could damage the voltage regulator.
13.8 Volts is what the original Bosch voltage regulators were set for. Some aftermarket ones are available with higher output voltages.
If your battery warning light circuit checks good using the procedure I mentioned and does not operate per your owners manual. I would suspect the voltage regulator has failed.

[SteinOnkel]

As Dieselspider said, check the B/V wire for 12V when the key is in the #2 position before starting. It connects to a male spade below the main alternator stud. Few other things to consider are 1. making sure the choke is properly adjusted, it should be fulled closed when trying to start the engine cold and open up and stay open as the thermostatic spring expands from the temp of the coolant getting hot. 2. Idle cut-off solenoid on the carb will close the idle jet passage unless it has 12V, which is coming from a thermostatic switch underneath the intake manifold. 3.Having the fast-idle mechanism connected does have some legitimate benefits, it will increase the idle speed to help prevent the car from stalling, can confirm that it does make the car easier to drive compared to my 83. Do you have a shop manual?

The video was made with the engine piping hot, hence the choke being open. It works just fine although the cold start does suck.

The Idle solenoid is an interesting topic though. I can hear and see it click when I key the ignition on. However I thought the switches on the bottom of the intake were for emissions junk so they are all disconnected. I wonder if the solenoid has multiple positions.

I've found these solenoids to be a pita most of the time, I'm going to get a short bolt with the same thread and put that in its place. That's going to be the last ditch effort on this crappy carburetor before I show it where the trash can in my workshop is. No way no how am I spending the time and money to get the bushings remachined that I suspect are leaking. I'm about 10 hours of labor into this carburetor right now and there's really no way to justify that. It doesn't flow very well at all and I hate the mechanical second stage, I feel like it opens up without any grace or poise and much too late.

As for the alternator, yeah time to yank it out and go to Autozone. Or - it being payday today - maybe just bin it and get a new one.

Cheers
Steiny

[DieselSpider]

Don't just bin it, have it tested to verify whether it actually is the problem. Even if it tests out bad you will still need to vet out the wiring to ensure that there are no other issues which caused the alternator to fail. You really need to have an accurate understanding of the systems your working with before you start pulling wires and such. Sometimes you have to slow down and reflect upon things before taking action.