Alternator redux-voltage regulator testing or ?

[RDM]

Many of you were great help in getting my alternator sorted (Red lights don't mean it's Christmas). Thank you! But like my children's rooms, it doesn't seem to want to stay that way. By way of reminder, I bought a rebuilt alternator from my local German mechanic Huwer Sportwagentechnik, installed it, and life was peachy.

On the way to work today, the red lights of death reappeared. I have 12.1 volts at key on, 11.5 volts at high idle, and 11.3 volts at high idle with the headlights on (all measured at the rear fuse box). Bentley says this indicates the alternator is toast, but before I take it out again I'd like to test the voltage regulator.

I've read on another thread that it's possible with a variable DC power supply, which I have access to (it's good to be a science teacher), but I'm not clear how to do that. The regulator has 3 terminals, D+ (alternator output positive, red/blue), DF (field coil positive, black) and D- (ground, brown). So how do I test the voltage regulator?

The second thing to do is to test the various output diode banks in the alternator. The instructions given here Pelican Technical Article: Alternator System Troubleshooting seem pretty clear except one thing: When it says to connect 12 volts to the DF terminal on the relay board, does it mean the voltage regulator connector, or somewhere else? Same question with shorting the D+ and DF terminals on the relay board.

To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.

To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere.

Again, thanks.

[RDM]

OK, so here's what the voltage regulator looks like opened up. Can anyone confirm for me that the tan component on top with the two red stripes is a diode? I think it is, but it passes current in both directions, so that would be bad.

Does anyone have a good source for these?

What sort of other problems would a poorly functioning voltage regulator cause? I feel like I've been battling electrical problems since day 1 with this car....

[HawgRyder]

That is a wire wound type resistor.
Red lines indicate "2" on the scale.
But you would need to see the third line to see if it's black or some other colour. (Black is zero)....which would mean 220 Ohms...sounds a little small...counld be 2200 Ohms or more.
Also...from the size...could be about a 5 watt resistor.
Anyone else have an idea of value?
Bob