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Alternator wiring harness- Diagnostic vs Heater Blower wire?
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72vwtype2
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Joined: February 10, 2006
Posts: 154

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PostPosted: Mon Jan 15, 2018 9:30 am    Post subject: Alternator wiring harness- Diagnostic vs Heater Blower wire? Reply with quote

My alternator wiring harness for my 72 bus where the plug (3 wire - brown, green red) connects to the voltage regulator on the fire wall has a black wire (diagnostic) attached to the red wire instead of the blue wire (Heater Blower).

The wiring diagrams indicate that it should be blue. It doesn't even show the black wire. The only reason I know it's a diagnostic wire is through the various postings on this site. I have seen pics on this site of both types of wiring harnesses, but I am not sure what the difference is.

Do I have the right wiring harness? If so, how do I wire my heater blower?

Thanks.
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Wildthings
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Joined: March 13, 2005
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PostPosted: Mon Jan 15, 2018 10:43 am    Post subject: Re: Alternator wiring harness- Diagnostic vs Heater Blower wire? Reply with quote

You must have the blue wire (or its equivalent) if your alternator is charging, it does not run through the alternator harness, but just comes off the plug.

VW changed the way the relay for the heater booster fan was triggered on the later Bays. Presumably this was for a reason, so you might copy the later bay setup. This may be what you already have anyway. Check out the wiring diagram for the '79 model year in the Samba Technical section.
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telford dorr
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PostPosted: Mon Jan 15, 2018 10:45 am    Post subject: Re: Alternator wiring harness- Diagnostic vs Heater Blower wire? Reply with quote

Quote:
If so, how do I wire my heater blower?


Per the drawing, of course!

Seriously, the schematic shows a black diagnostic wire connected to the big red wire at the alternator, but anything relating to the diagnostic connector can be either ignored or removed, as there is virtually no chance of it ever being used again (unless someone has access to a mating plug, in which case I'm interested...]

The blue wire from the regulator is used as a power source for the blower relay, supposedly to keep the blower from running unless the engine is also. That power passes through the relay coil and grounds at the switch contacts at the heat control levers (brown/white wire). When the relay closes, fused battery power from the starter motor battery connection (red wire) is fed to the blower motor (yellow/black wire).

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