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Old April 27th, 2013, 14:58   #1
A4-TDI
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Default MK4 ALH alternator pinout?

Just a simple question about the pinout of the small connector of an ALH alternator. I'm asking this because after my engine rebuild I decided to replace my old alternator, the connector and alternator itself was broken due to the accident of the engine donnor.

Now with my new jobber alternator, I don't know which pin on the 2 pins are the 'L' and 'DFM' terminal because there are nothing written on the alternator. The 'L' terminal goes to the cluster and DFM terminal on the ECU.

The connector have a round shape on one side and squared shape on the other side. Which side are the DFM and L ?

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Old April 27th, 2013, 17:20   #2
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Someone?
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Old April 27th, 2013, 17:54   #3
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The DFM wire is Brown/Red................ goes to 121/38, ECU

The L wire is Blue..............goes to T32/12, Cluster
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Old April 27th, 2013, 18:03   #4
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I know, but I installed a new connector on the wiring harness. There is a 'D' shaped connector. I plugged the brown/red wire (DFM signal to ecu) on the square side of the connector, and I plugged the blue wire (L signal to cluster) to the round side of the connector. The alternator (new rebuilt one) overloaded the voltage (17 volts!) and after 4 seconds, it stopped to charge. I'm really wondering if the DFM and L were plugged to the good side of the alternator plug...

I don't know if the rebuilt alt was bad or it's because I reversed the terminals. Will need someone that coulds check in his own car which wire go to round side and which wire to square side.
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Old April 27th, 2013, 18:10   #5
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Give me a few minutes ........... I'll go check!
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Old April 27th, 2013, 18:20   #6
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Round side is T2e/1 ---- DFM < The pin reference at the 4-pin connector is T4/1

Square side is T2e/2 ---- L < The pin reference at the 4-pin connector is T4/2


The 4-pin connecctor is located at/above the starter. The other two pins are T4/3 and T4/4 which involve the AC Compressor.
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Old April 27th, 2013, 18:21   #7
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Typcially high voltage will cause the Cluster to shut down for protection.
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Old April 27th, 2013, 18:40   #8
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do you think the alternator is blown now? I was unable to have the information, so I went to a junkyard to have a new connector from an 1.8t alternator and in this case, the blue wire was on the round side. I connected the cluster to the DFM terminal of alternator and connected ECU to the L terminal of alternator because there are no indications of DFM or L in the alternator... Hope nothing have broken...

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Old April 27th, 2013, 19:06   #9
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Well, in this case, I'd be concerned about the ECU .. I hope the engine will start and run.

Most likely a diode has bit the dust in the ALT.

A couple of years ago, I did a TB job on a 99.5 Jetta. The dude wanted the engine pressure washed when I got finished. Well, during the test drive the Voltage spiked several times. Each time, the Cluster would go dead. I shut the engine down for inspection. When I restarted the engine, the cluster would be fine. Revving the engine would spike the voltage, cluster would go dead. Back at the garage the volt meter showed more than 17 volts when I revv the engine up above 2000 rpms. I began to smell battery acid. Luckily, his rebuilt ALT was still under warranty.

The information I posted was from the Bentley Manual covering a 2002 engine and the engine in my Vanagon, which is a 2002 ALH. I cannot imagine VW changing the color code on the ALH production. It may be different with the 1.8T ..
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Old April 27th, 2013, 21:43   #10
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Engine runs very well, no problem. I will reverse the wires tomorrow and see if it charges or not. If not, the alternator is under warranty...
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