Technical Fiat 500 alternator removal!!!!

[GettinBetter]

With reference to your post #38 above....
This is my main car, and here's where I took it last year.. 6725 miles.

Trip Around Europe

 

[HWMAX]

Well the new alternator iS in and working. Regarding the differences between the two types of alternator I have attached some pics of what I am getting on the D+ terminal of my new alternator. These cover 3 states, IGNITION OFF, IGNITION ON BUT ENGINE NOT RUNNING and IGNITION ON AND ENGINE RUNNING.
The IGNITION OFF image shows about 0.4 Volts AC which is just some noise being picked up.
The IGNITION ON BUT ENGINE NOT RUNNING image shows DC pulses of varying amplitude and duration.
The IGNITION ON AND ENGINE RUNNING image shown a steady 13Voly DC signal.

I would have some doubts about alternators with the small D+ threaded stud terminal being interchangeable with an alternator with the Lin + plug and socket terminal even if you altered the connections to suit. One thing I am pretty sure about though, if the alternator fails again I will be glad I fitted a test lead from the D+ terminal. It means I can check this terminal without even having to to anything other than open the bonnet

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[HWMAX]

Thought Id include a couple of pictures of the car.

 

[GettinBetter]

So I'm assuming your car originally had the D+ connection?

IMO, this traditional field connection would also be controlled by the Engine ECU, albeit the current flow would be far larger than the LIN which the ECU would have to deal with (by adding components external to the processor). Whether this is the reason for changing to intelligent types of alternator or not who knows?

 

[HWMAX]

Yep, it was originally the D+ connection. When I ordered a used replacement from ebay (before I removed the old one) I was sent one with the Lin+ connection. It was only when I went to remove the old one I cottoned on to the fact the connection was different. At that point I decided to get a new one anyway as the job as such a pain. Having removed the old one I could easily see the manufacturers numbers which gave me confidence when ordering the new item.

As far as the D+ signal is concerned the alternator seems to be getting a continuous 13V, maybe a simple ON/OFF situation. In 5 minutes running the signal was constant. As for what is going on when the ignition is turned on without the engine running I am not so sure. Maybe the ECU is checking the circuit for impedance or some other health check but I honestly have no idea.

 

[GettinBetter]

... When I ordered a used replacement from ebay (before I removed the old one) ...

Ah yes, that's fatal now days, I won't order nowdays till I'm completely sure, which is made all the more difficult but the lack of real dimensional info on websites these days. The guy on ebay, that I got mine off of, contacted me by message and asked what connection I had. Although it didn't stop me getting the wrong start motor, which I decided to replace at the same time. There are two hole and three hole fixings and both have completely different hole positions.

... As for what is going on when the ignition is turned on without the engine running I am not so sure. Maybe the ECU is checking the circuit for impedance or some other health check but I honestly have no idea...

Nor me.

Good that its working though, well done and thx for posting results.

 

[HWMAX]

Glad its sorted. This site has helped me so many times I am happy to contribute what I can. Thanks to everyone on this site for the hassle and money they have saved me over the years.