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Electrical: Engine Starting, Charging
4. alternator frame, then
5. Blue wire to engine ground.
These bulbs supply the required pre-excitation current to begin alternator charging:
Battery light
Parking Brake
Brake Warning
Bulb Failure
You can test for power to and thru the bulbs to the alternator D+ terminal by
taking the red wire off the D+ terminal and holding it to any engine metal (not
the alternator itself) while a helper turns the Key ON and observes the warning
lights.
Lights ON? = all is well to and thru the D+ wire
No lights = check for battery voltage at disconnected red wire end
+12V present? = battery=>cluster=>D+ wire path OK (problem is in #1 thru
#5)
No +12V = problem between battery and +12V side of cluster circuit
Installing a Replacement Exciter Circuit to the Alternator. Is it possible - and
if so, is it wise - to run a wire from the battery's + terminal to the back of the
alternator? Or, does that create a risk of damage in the long-term"? [Steve] This
information relates to my experience with the Denso 100 Amp alternator which is
on both my wife and son's 940.
It may or may not apply to other model alternators. It's possible, but not wise to
make a hard connection from the battery positive to the excitaton circuit on the
alternator. You would only do this if the circuit on the back of the flexible
instrument cluster PCB failed.
The reason(s) are:
1. You wouldn't have the convenience of a charge light to tell you that your
alternator is charging.
2. The excitation circuit (originating in the instrument cluster and going directly to
the alternator via the small red wire) powers directly to the internal voltage
regulator.
This allows the charge light to illuminate. The voltage regulator provides a circuit to
ground to excite the alternator field windings until the alternator begins charging.
After the alternator begins charging, the voltage regulator opens this circuit and the
alternator continues to provide its own field (excitation) voltage. If you connect a
wire directly from battery positive to the alternator excitation terminal, you will
have a constant drain of the battery, and probably damage the voltage regulator
over time.
On my son's 940, I did run a separate wire to the excitation terminal but not from
the battery. I ran this wire from a "switched hot" source under the dash and on to
the alternator. Inside the car, I pulled a loop of this wire out of the dashboard, cut
it, and soldered a light bulb holder for a standard 1034 12V light bulb into the
circuit. The hot wire is soldered to the terminal next to the center contact on the
bulb. This did three things: it gave me a "idiot light" to tell me if the alternator
file:///C|/Users/Steve/Documents/Volvo%20FAQ%20Updated/ElectricalStarting.html[01/13/14 10:02:47 PM]
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