1980 928 alternator replacement questions
05-17-2017, 02:28 AM
#1
Track Day
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1980 928 alternator replacement questions
As mentioned in the other thread, the alternator did not work on this 928. I tested voltage with the car running, both at the battery and at the alternator, and it read about 12.2 volts - likely the amount of charge in the battery.
The alternator in the car was a Bosch 0120484 017 unit. The only unit that I could find locally for the 1980 928 is a rebuilt unit with the number 13122. So I bought that. The new alternator is physically larger than the old one, although it fit the mounting brackets. The main wiring connections are higher up on the new alternator than on the old one, but that worked OK.
After installing the new alternator, at first the car still did not charge.
I had noticed that one difference between the two alternators is that the old one has no connection for an exciter wire, while the new one has a yellow wire and plug coming off of it that must be for an exciter wire connection. I could not find a connection on the car for the exciter wire, until I recalled that a few days ago I had found a wire without an end in a red sleeve with another wire in it that connected to the sensor (sensor with two finger tightened nuts for the connections on the bottom) next to the alternator. I had assumed that the loose wire had come out of the connector to the sensor and had just connected it there.
Putting two and two together, I disconnected the wires from the sensor and hooked one to the exciter wire. By this time I did not recall which of the two wires was disconnected a few days ago; one wire is dark blue or black and the other is blue and yellow. So I connected the blue and yellow wire to the exciter wire on the alternator. (I tried both wires, one after the other, and both work, although the warning lights on the dash and center console flash when I connect the blue or black wire. The lights don't flash with the yellow and blue wire connected, which makes me think that is the correct one to connect to the exciter wire on the alternator.)
SUCCESS: With the exciter wire connected, the alternator charges at about 14.2 amps, which sounds about right, I would guess.
A few questions remain:
1. Can anyone tell me what that sensor/unit next to the alternator is for?
2. Did I pick the right wire - blue and yellow - to connect to the exciter wire on the alternator?
3. Can the old alternator that I took off ever have worked without an exciter wire connection? Possibly it has an internal link from the positive connection to the internal exciter? Maybe it never worked and maybe it is intended for another application?
4. What might I be missing here?
The alternator in the car was a Bosch 0120484 017 unit. The only unit that I could find locally for the 1980 928 is a rebuilt unit with the number 13122. So I bought that. The new alternator is physically larger than the old one, although it fit the mounting brackets. The main wiring connections are higher up on the new alternator than on the old one, but that worked OK.
After installing the new alternator, at first the car still did not charge.
I had noticed that one difference between the two alternators is that the old one has no connection for an exciter wire, while the new one has a yellow wire and plug coming off of it that must be for an exciter wire connection. I could not find a connection on the car for the exciter wire, until I recalled that a few days ago I had found a wire without an end in a red sleeve with another wire in it that connected to the sensor (sensor with two finger tightened nuts for the connections on the bottom) next to the alternator. I had assumed that the loose wire had come out of the connector to the sensor and had just connected it there.
Putting two and two together, I disconnected the wires from the sensor and hooked one to the exciter wire. By this time I did not recall which of the two wires was disconnected a few days ago; one wire is dark blue or black and the other is blue and yellow. So I connected the blue and yellow wire to the exciter wire on the alternator. (I tried both wires, one after the other, and both work, although the warning lights on the dash and center console flash when I connect the blue or black wire. The lights don't flash with the yellow and blue wire connected, which makes me think that is the correct one to connect to the exciter wire on the alternator.)
SUCCESS: With the exciter wire connected, the alternator charges at about 14.2 amps, which sounds about right, I would guess.
A few questions remain:
1. Can anyone tell me what that sensor/unit next to the alternator is for?
2. Did I pick the right wire - blue and yellow - to connect to the exciter wire on the alternator?
3. Can the old alternator that I took off ever have worked without an exciter wire connection? Possibly it has an internal link from the positive connection to the internal exciter? Maybe it never worked and maybe it is intended for another application?
4. What might I be missing here?
05-17-2017, 08:34 AM
#3
Team Owner
the exciter wire for the alternator is lite blue it originates from pin 1 at the 14 pin connector.
I would verify continuity of this wire from the 14 pin connector to the alternator end before connecting any wires ,
Based on your info you have connected oil pressure sender wires to the alternator .
NOTE Adding pictures will greatly aid in the more accurate diagnosis
I would verify continuity of this wire from the 14 pin connector to the alternator end before connecting any wires ,
Based on your info you have connected oil pressure sender wires to the alternator .
NOTE Adding pictures will greatly aid in the more accurate diagnosis
05-17-2017, 08:36 AM
#4
Team Owner
try this