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Electrical: Engine Starting, Charging
the circuit. A simple continuity test on the meter will do the job. If you have a
failure, the Bosch regulator/brush pack unit is easy to replace with the alternator in
the car. If your battery has been overcharging, it can boil off electrolyte and may
need to be topped off.
Exciter Current Through the Warning Lamp on the Panel. The alternator
(charging) warning light in the instrument cluster feeds a small amount of electrical
current to the field coils in the alternator when you turn the key on and the engine
isn't turning. This excites the coils (electromagnet) and the alternator gets the
magnetic field it needs to start charging as soon as the engine runs. When the
alternator isn't charging at all (engine stopped) that wire to the alternator also
provides a ground path for certain warning bulbs in the cluster, so they light up.
Diodes in the network keep current from backfeeding into unwanted circuits. So if
you have a bad connection for the alternator warning wire, the alternator won't
start charging right away. But most alternators will self-excite once the revs get
high enough (say 2000 engine RPM) and then they stay excited and charging, even
at idle RPM.
[Editor] To initiate charging upon startup, the
voltage regulator must be at 12 volts. If this is grounded or disconnected (as, for
example, through a loose instrument panel or chassis connector), your alternator
will not charge. The idiot lights may or may not go on, but if they do and they
remain on, then suspect this wire or the panel connector for faults. You can also
rarely experience a
sure the alternator warning lamp bulb is not burned out.
[John Randstrom] If you pull the wire off the alternator that comes from the dash
board charging lamp and ground it, the idiot light should light with the ignition in
the run position. If the lamp does not light then there is a problem with the bulb,
the ignition switch, or the wiring/instrument cluster circuit. An easy way to see if
this circuit is causing your no charge situation would be to connect a wire from the
battery positive terminal through a small spare idiot light bulb(or any bulb with the
same wattage and voltage specification) to the idiot lamp circuit connector on the
alternator. The alternator should charge and the lamp should light when the engine
is off, and go out when the alt. starts charging just like the original dash lamp
should do.
[Tip from Paul Golden] I removed my instrument cluster and did the continuity
checks, sure enough the solder joints had come loose from the wiring. I fired up
the soldering iorn and hit each solder joint with some fresh 50/50 flux core solder.
Installed the instument panel and presto, all the lights work once again. Since then
I have repaired that same problem in 6 different cars, 760, 3-960, 2-940 so it
seems to be a regular problem.
Diagnosing Alternator Exciter Circuit Troubles. [Bruce Young] The Battery,
parking brake, brake warning, and bulb failure lamps should all iluminate when the
ignition switch applies battery +12 to one side of all 4 bulbs and the other side
finds a path to ground via that small red exciter wire from the panel to:
1. alternator D+ terminal, then
2. voltage regulator, then
3. alternator brushes and slip rings, then
file:///C|/Users/Steve/Documents/Volvo%20FAQ%20Updated/ElectricalStarting.html[01/13/14 10:02:47 PM]
flexible circuit board failure
small wire
going into the rear of the
on the back of the panel. And make
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