Going through my junk, I have a few regulators to choose from.
Two are Bosch RE55 (out of Bay kombi), one is RE57 I think from a Beetle.
Are they interchangable?
Any way to test them?

Also I have different one, see pic, also out of a Kombi. This one has 3 pins rather than two in Bosch, what happens with the third pin?

My '76 kombi has a 3 pin regulator with the same pin designations as the one in your second picture (except mine's a Bosch). The D+ goes to the +ve output on the alternator, the DF goes to the field coil on the alternator (which controls the alternator output), and the D- goes to earth.

HTH

I may be wrong but I believe the extra lead goes to earth, where i expect the two pins have an internal earth...
then again My Bosch alternator has an internal regulator...
I can't remember whether My Son's Beetle has 2 or 3 pins...

Lee

Cool, thanks.

So does any one know the difference between Bosch RE57 and RE55??

The external regulators don't seem to last that long.
My Son has used a few on His Beetle with an Alternator that uses an external regulator. Its the same with other vehicles I have owned over the years. Internal regulators seem to be better built or maybe larger or stronger, I don't know..
But I know which one I would rather have...

Lee