Yes, as other posters have pointed out (and your) your numbers look good when its working but bad when its not. I'd replace it the regulator with a new one. They're cheap enough.

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(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Use a DC voltmeter, preferably a digital one. Measure voltage at battery with engine off. It should be somewhere in the area of 12 volts. Now start the engine and measure again. If the voltage goes to about 13.5 to 14.5 or so, then the alternator is charging. If it does NOT go to these voltages, the problem is wiring, alternator, or voltage regulator.

Trace the wiring back to the voltage regulator and check for voltage there. If you still don't have the higher voltage range, try changing the voltage regulator. It costs about fifteen bucks and you can change it in fifteen minutes.

Hope this helps.
Whip

Turns out that alternator has an intermittent failure; Probably why I didn't know there was a problem for so long. Had it tested at 2 autopart stores: advanced auto's machine said stator failure (?) ; autozone said it passed- so I asked him to re-test, passed again, ...re-test, failed!
I'm using my backup alternator for now.

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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI