HI again,

It seems that the instrument cluster going erratic is a good clue to the possible lack of charging.

There is some truth that the instrument cluster effects the running of the car. Especially if the VSS is used by any ECU. Past that, it should not kill the engine.

You could have two things going on with the circuits on the instrument panel.

The exciter wire current comes through the the cluster and some diode circuitry containing the various lights. If you look into an instrument diagram you will a network of diodes to prevent back feeds under different circumstances of what light gets energized.

The exciter wire has to have the bulb working "in circuit" to complete the current path to the alternator. It acts as a current limiter as you only want or need a trickle of current going through to the regulator.
The output is passed on to the brushes to bring up a magnetic field voltage in the stator. This produces a more feed to the regulator. The regulator that takes over by scooting up the current output along with the voltage being monitored or controlled. All a self regulating system.

When this stator voltage exceeds the battery voltage coming down from the cluster the light goes out since its ground circuit is through the alternator.
It does take much to turn that light out as its only voltage pressure equalized that turns out the lights current flow.

You need to observe a voltage at least 1.0 to 1.5 volts above the original standing voltage in order to push current into the battery. These variances take place on what rate the battery absorbs the current. A battery really low or has a bad cell will affect the alternators output and its own life expectancy.



There is also a voltage regulator on the board that stabilizes current to the gauges so maybe it's not getting power to it continuously to control swings of the gauges.
Still with all this said, its like Art said, it comes down to connections or wiring.

I think you need to check the exciter wire for voltage with the key on in position two and the engine not running.
I don't know what voltage you should have there exactly, I have never checked it for the fun of it.
But I expect it will be "less" that what ever standing battery voltage on the battery is at the time.
FYI, a 12.35 voltage is an indication the battery is very flat. 12.65V is full so note the differences for a on going maintenance type of heads up.

So now, the exciter circuit, with its diodes, is going to be about one volt less plus a slight voltage drop through the light bulb. If your readings not up in that ball park area, on the exciter wire out at the alternator, you got a problem.
Worse case, I might expect about ten volts plus to be normal.

You want to check for voltages from two ground points and from the battery negative.
One is Engine ground and the Alternator housing. It would not be the first time that errors are located in these areas. It cross and back checking. Even taking same side voltage "zero" checks are good troubleshooting techniques.
If you are getting that battery voltage to the alternator it has to work, since it tested to be good.

In your case you might want to Add in some corrosion or loose wire connector points as things must be going down hill fast to kill an engine. Not charging or not getting the charge going out is a big problem for the whole system.


I'm not sure how the alternator connects to the cluster. Maybe it's through the gray connector on the firewall. The power side could be problem inside the fuse panel side of things or even out at the fender junction box.

Keeping your eye on the voltage of a battery and by observing the total system with a "dash" voltmeter helps. Take note of its response to loading or draining, like starting, conditions can give you a heads up on the shape or condition of both!

A Voltmeter is a great friend to get diverse with.
It is enough to make Art a betting man! Wow!

(:-) Happy New Year!
Phil