[Vwdiesel] gas truck to 1.9td project finally drawing to a close..

Sandy Cameron scameron at compmore.net
Thu Mar 18 10:20:01 EST 2004

Did I screw that one up??
The red wire is the tach wire, goes to the W terminal which internaly inside
the alternator, I believe, is attached where the inner ends of the 3 phases
are joined together in the Y configuration.

The Blue wire is the field start-up excitation which needs a little bit of
12 volts through a smal lamp or resistor when the ignition is turned on.

The red thick wire(s) go to the battery + terminal, usually via the starter
battery terminal.

On 90A alternators, the + terminal is a bolt with nut, and usually only one
thick cable.
On 65A alternators, there is a 3 prong plug, the 2 big ones are power out to
the battery, and the small one is the blue field wire in.

I'll have to go out and check my A3 to see what they did with the alternator
output, as on the A3s, they brought all the engine wiring to a single ratty
connector to make assembly quicker. ( No cultural aspersions here) They may
have brought the alternator output through the connector on 2 lesser wires.
I quickly cut the 2 wires they used through the connector to feed the glow
plugs, and rewired it like an A2, along with the 4 independant plug wires
brought up to an accesible common point in front of the injector pipse( to
make open plug investigatios painless). As auto manufacturing becomes more
driven by economic assembly requirements, more and more strange things are
seen under the hood and the dash.. No other explanation for the insanity...


At 06:34 AM 3/18/04 -0800, you wrote:
>Well, the VW diesel has that little blue wire too and
>its NOT the wire for the "W" (RPM terminal) on the
>alternator. Its for the other little terminal, the one
>next to the big lug that alternator power is tapped
>from. (B+ or D+?). I think its wired to the alternater
>charge warning LED in the cluster and provides the
>excitation current. The "W" terminal on the diesel
>alternator is hooked to the upshift control module,
>dynamic oil pressure control unit (The tiny circuit
>board for this sits next to the speedometer INSIDE the
>instrument cluster and the one used for gas engines IS
>DIFFERENT than the circuit board for diesel
>applications, although they look almost identical
>(Don't ask how I know this!, the cause of another
>unnessary instrument cluster removal after I swapped
>in a speedometer from a gas Jetta with the circuit
>board attached! Close examination revealed that they
>are indeed different and the warning circuit in the
>diesel will not work with the boaed from a gasoline
>engine) and to the tachometer on turbo diesel models.
>The large red wire conects to the positive battery
>terminal, I think the connection is at the starter.
>--- James Hansen <jhsg at sasktel.net> wrote:
>> One multiple question if you will...
>> Finally getting the 1.9td into gasser truckie
>> project finished and I have
>> one small obstacle.
>> Had the fire lit today, sounds nice with no exhaust
>> system on, turbo really
>> howls :-)
>> I am totally without a wiring diagram for a gas
>> truck.  Everything else from
>> diesel truckie to Passat, but no gasser truck
>> diagram... so...
>> The hitch is the alternator- a motorola, which is
>> now a Bosch 90amp due to
>> bracketry- had to use the A2 setup. The wiring is
>> different, and I've never
>> done a Motorola to Bosch swap before... and I've
>> never had a motorola apart
>> before either to see what is what.
>> The wires are two largeish red, one blue all 
>> terminated at the alt plug,
>> and one small red one by itself. Big red ones I
>> assume are to power- is this
>> via a load reduction relay, or what?  No power at
>> them at present- or chase
>> some popped fusible links?
>>  The blue one is for I'm assuming the dynamic oil
>> pressure sensor system-
>> when I power it, the oil pressure buzzer goes off
>> with the key on, so I
>> assume it is to let the module know when the engine
>> is on or off by voltage
>> from the alternator.  This right?  With a bosch, is
>> there a quick and dirty
>> way to control the power to the dynamic module?
>> relay controlled by what
>> exactly...? hmm...
>> small red wire is.... alt light?
>> These questions and probably more...
>> there's a whole mess of purple and green ones that
>> used to be for the
>> transmission, terminate at the trans plug. I used
>> the backup light ones, but
>> guesses on the function of the rest?
>> Many thanks
>> -James
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