Engine Compartment Wiring
(Without CDI or CompuFire)
Wiring for both internal and external voltage
regulators is covered in this article.
The following topics are discussed in this article -
Engine Compartment Wiring
When a short in the wire to the backup lights burned out the ignition
switch and shut him down, Dave decided that it would be prudent
to rewire the whole engine compartment, since he found a number
of other areas in which insulation had either worn off or burned
off the wires. The "stock" wiring arrangement in the engine compartment
(no CDI or CompuFire) is shown roughly in the following diagram.
(See more on the "Stock" Coil/Distributor Wiring below.)
Rough Schematic of Engine Wiring
In process of this engine re-wiring job, Dave installed what he
calls a "power block" on the left fresh air nozzle to keep all of
the wiring straight. Following is a very rough wiring diagram showing
the wiring layout on the power block, followed by a photograph of
the power block after the engine compartment re-wiring was complete.
Power Block Wiring
The Power Block
New Engine Wiring
Not long after completing his engine re-wiring, Dave accidentally
pulled the wire to the automatic choke loose when the key was on
(Dave had just completed timing the distributor); the wire, which
was hot, of course, fell down and shorted against the alternator
-- causing the ignition switch to burn out AGAIN! To prevent this
from happening in the future, it was suggested to Dave that he put
a 25-amp fuse in the wire that goes from the ignition switch back
to the engine compartment, right near the switch at the plug. Such
a fuse, the guy said, "will power everything, but blow if something
screws up, which will kill power to the sensitive stuff. Better
to replace a fuse that a switch."
A good idea. Dave has now replaced his ignition switch again for
the second time and has installed a 25-amp fuse in the wire from
the ignition switch, just "upstream" of the power block he installed
in his engine compartment.
"Stock" Coil/Distributor Wiring
(No CDI or electronic ignition)
The black wire coming into the positive terminal on the coil (#15) is from fuse #12, which receives power from the ignition switch. Note three black wires leading from that terminal - one to the automatic choke, one to the backup lights, and one to the idle cut-off valve on the carburetor. The positive terminal on the coil is just a convenient place to obtain power to these three components. The fact that these components receive power from a terminal on the coil has nothing to do with the operation of the coil itself. The three wires could each go up to fuse #12 individually, but that would be very inconvenient. So VW chose this configuration.
You may have to get creative about how you attach so many wires
to the single terminal on the coil. Any auto supply store can sell
you a little T-shaped adaptor that will fit on the terminal, with
three "wings" (if you will) to which the three black wires can be
Please be sure to use black wire for this purpose -- black means "power
when the ignition switch is on" in the VW world.
Alternator with Internal
When wiring an alternator with an internal voltage regulator, remove
the blue and green wires from the old external regulator and splice
them together. Run the green wire to the (D+) terminal on the new
alternator. This provides the wiring to the indicator light, which
is an essential sensing part of the alternator internal wiring.
See the wiring diagram above ("Rough Schematic of Engine Wiring") for the alternator with an internal
Engine Compartment Wiring
(See also Alternator
Alternator with External
This wiring diagram is courtesy of "Speedy
Jim," the smartest person we know when it comes to VW electrics.
Converting from an
External VR Alternator to One With an Internal VR
The following was written by Rob Boardman.
When wiring your new alternator with an internal voltage regulator,
you must disconnect BOTH wires from the (B+) terminal on the old
external voltage regulator, but keep them spliced together (they
should currently have a double spade connector on the regulator),
and then add the red wire from the (D+) on the regulator to make
a three way splice.
In the process the red wire that WAS on the (D+) gets moved to
the (B+) terminal. Since the voltage regulator is now internal,
you just bypass the old regulator with the red wires. (You might
need to put an small extension in this wire if it's not long enough
to meet the other two -- if so make sure it's of similar thickness).
All of the red wire is 10-gauge (larger). "Speedy
Jim" reminds us that you need to have substantial connectors
for this job. In Australia the hardware stores sell 240-volt screw
type connectors in either 15amp or 30amp varieties. There are two
types -- single hole where the wires are twisted and poked in the
one hole and the screw tightened (these usually have a nice soft
plastic cover over them -- self insulating), and a block type where
you can poke in wires from either end and screw two screws up to
tighten each wire. This type has the lower amp rating.
I'm not sure what you'd have in the U.S. with your 110-volt standard,
but choose the heaviest and it should be fine. The "single hole"
type are particulaly good as you twist the wires before poking in
the hole. This means the screw just jams the wires together and
the brass "bolt" doesn't actually carry much current. In the double
ended type, the brass block carries all the current from one wire
to the other.
My reason for saying this is that the red wires carry up to 50
amps, so they should be the single hole twisted wire type if you
can get them -- these are less likely to be a resistance point in
the circuit. The thin wires can be any screw or clip connector,
since that carries only a small current.
Necessity for the
Alternator Warning Light
It is absolutely essential that the (D+) terminal on the alternator
be connected to a functioning "Alt" warning light in the instrument
cluster. If this light is missing or defective, the alternator will
NOT charge the battery! See my hand-drawn wiring diagram above.
Also see Speedy
Jim's diagram, which is much better than mine!
The system is very simple, but it's absolutely critical that you
get it right. The (D+) terminal on the alternator MUST connect to
a functioning warning light in the instrument cluster. There should
be just one wire (blue) from the (D+) connector on the alternator
to the button on the bottom of the normal indicator light in the
dash. The dash light is also wired from the (D+) (Blue) to ignition
terminal #15 on the coil, which in turn is connected to the positive
(+) post on the battery (Black). There is no ground wire on the
light; the body of the bulb is connected to ground via the light
holder (which also provides the ground connection for the other
dash lights as well.) The three bulbs (ALT/OIL/TURN) all have a
common connection in the socket which goes to ignition terminal
#15 on the coil (which receives power from the (+) post on the battery
by way of the ignition switch).
The alternator must get a feedback current through the "Alt" lamp
in the instrument cluster so it can sense the battery voltage; it
uses that as part of the alternator's internal circuitry needed
to charge the battery. In other words, with the ignition on but
engine off, the indicator light sees 12 volts from the battery (via
ignition terminal #15 on the coil) and glows, but with the engine
running, it sees 2 volts (14 volts minus 12 volts) running the other
way, from the alternator. It doesn't glow (needing more than 2 volts
to do that), but the alternator still "sees" the connection to the
So -- If the Alternator is charging, the (D+) terminal has 12 volts
on it; the blue wire from (D+) carries 14 volts to the "Alt" light
in the instrument cluster. When the engine is running, there is
12 volts on the *other* side of the lamp from ignition terminal
#15, so potential difference is only 2 volts and the bulb doesn't
light. But, if the alternator dies or the drive belt breaks, there
is no voltage on (D+) (looks like ground) and current flows from
#15 thru the lamp to (D+), and the "Alt" lamp comes on to warn the
driver of a problem.
An LED light won't work for this purpose. LED's are diodes and
will not allow current to flow in the opposite direction. With the
LED, it would see the 12 volts, but the reverse flow 2 volts would
be stopped by the diode nature of the LED, so that wouldn't work.
The 12-volt 2-watt indicator bulbs are available at any VW parts
store. The same bulb is used for the speedometer illumination bulbs
(two of them) and the other indicator bulbs in the instrument cluster.
In a pinch you can borrow one of the illumination bulbs to replace
a blown Alt indicator bulb -- the speedometer will be a bit dim
on one side but can still be seen until you get a replacement bulb.
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