Uncle Andrew,

I'll guess you mean the dash light illuminate while the engine is running, yes? Sort of like when you turn the ignition key lock to the second (or third?) dentent where the dash lights illuminate just before you start the engine.

The lights flicker on and off as the engine runs, or the lights remain on after the engine starts, yet the lights go out after the engine reaches about 2500 RPM or a little more? (See exciter wire voltage failure in other articles you search the bb for.)

First diagnosis is verifying the alternator. A quick prescription is that the brushes in the brush carrier / voltage regulator assembly are so short now that they bare touch the stator (or armature) rotor contacts. You remove the voltage regulator / brush carrier from the rear of the alternator and if the two grey-silvery-bronze square brushes extend barely a few millimeter at their lowest point in the recessed arc beyond the plastic-like brush carrier housing, replace them.

You can verify the condition with a voltmeter. If, with a cold engine, you are not seeing around 14 VDC (14.5 is optimum) and, with the engine warm, about 12.5-13 or VDC, the battery alone electrically powers the engine; depleting the battery.

Please purchase the Bosch brand brush set. Bosch PN 11011. The aftermarket offering offer inferior brush material and the springs are usually too stiff.

You may want to inspect the alternator. Dunno how many mile you have. The rear alternator stator assembly bearing fails first from exposure to the exhaust port (manifold) heat. So, you may want consider alternator replacement. A Bosch or SEV Marchal alternator is usually good for the life of two sets of brushes, more of less; first set from the factory and the second set the owner replaces (or has replaced). The alternator may make squealing sounds some 100,000 miles or twice that after the second set of brushes.

Finally, you may want to inspect the wire harness that connects the alternator wiring that routes underneath the engine behind the crank pulley. Two flat springy bendy metal retainers secure the sheathed harness here. If the front engine or timing cover gasket leak oil, if even slowly, the insulation deteriorates and become stiff. This can form a nasty electrical short as the heavy cable with red insulation connects directly to the battery.

A search of articles on the brickboard and in the FAQ here can suggest alternate routing methods to dress the cables that connects to the alternator and the oil pressure switch.

The other cause may be a failed voltage regulator. These voltage regulator fail rather instantly from a component diode in the rectifier inside the alternator. Another cause may be failing field coil windings of one or more of the windings; usually on the rotating stator.

Questions?

Hope that helps.

Respectfully,

Buttermilk and Carrot Cake.
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