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Alternator Wiring


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Hi guys, I hope you all had a great christmas break, but now its back into the tech:

In the quest for a higher current Alternator i bought a 140amp jobbie off ebay direct from a local Audi dealer. Its a genuine Audi/VAG part and is branded Valeo on the rear cover, all good so far, but the problem is the connections.


As you can see from the picture below it has a large terminal post for the batt+ but the other connections are in a 2-pin multiplug and are labeled "L" and "DFM", does anyone know what these acronyms mean, are they directly analogous to the sense and waveform terminals found on normal alternators? Or have I accidentally bought an ECU controlled alternator that cannot be made to work off the battery sense wire like a normal alternator?


Any help would be gratefully received


Lewis :)

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It looks identical to the Nippon Denso that I have just changed on the Cherokee…………… L to the ign light and DFM is the Field output load sensor that is controlled by the ECU. This is for a soft start to the alternator.

I’ll investigate the soft start further, but I am fairly sure it’s to stop the alternator putting sudden load changes on the polyvee drive belt as this would cause belt chirp. Some of the alternators (like Jeep) also have a clutch driven pulley to take out the overrun deceleration inertia of the stator onto the drive belt.

I seem to remember that you can leave DFM disconnected as it is an output from a V FET within the regulator, which is one of the newer ‘smart multifunction regulators’

this is from an application sheet




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