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Alternator and Regulator Wiring Diagrams, TDV6 and petrol V8 and V6
This is a three page pdf that shows the alternator and regulator wiring for the petrol V6, petrol V8 and TDV6. The pdf can be either printed or by right clicking on the displayed pdf, rotated as required for viewing.

Of interest is that the regulator gets its instructions primarily from the Engine Control Module (ECM) and only secondarily from the vehicles electrical buss. The conductor from the battery thru the 5 amp fuse F20E is to provide initial power to excite the alternator at startup and then secondarily, to instruct it if the PWM signals were not available. Primary instructions to and from the ECM are thru the two other conductors via a digital like Pulse Width Modulated (PWM) signal.

If F20E, the 5 amp engine compartment fuse box fuse is blown, the red alternator light on the dash will be illuminated. This means that the alternator could be OK, but if the F20E fuse is blown, no electricity will be generated. Hence check the F20E fuse if you get a red ALT light or some indication of the alternator not working.

Regarding operation of the red ALT light on the dash, it is not the regulator within the alternator that tells the red light to illuminate, or not, but instead the ECM. This is the reason the red light does not function in the same manner as with older vehicles. With the 3, sometimes you have illumination and sometimes not depending upon what the ECM is thinking. What this means is that you can have an alternator that is failing but the red light does not illuminate as the ECM is compensating for reduced alternator output - maybe by draining the battery and or cutting back on vehicle electrical loads such as shutting off or cycling the radio amplifier or heated seats.
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