The alternator light on the dash glows when the car idles. When you rev the engine it goes out but returns at idle. Is this the brushs or the regulator? OR any ideas?

The ALT light glows whenever the alternator output falls below the battery voltage. This is accomplished by having a diode in the instrument panel wiring that only allows current through the light in one direction. That is, the light does not glow when the alternator output exceeds the battery, which is the norm. The Alternator output should measure 13.75 to 14.25 volts depending on the ambient temperature. Lower temp., higher voltage. If this is ok then the alternator output has pulses in it which fall below the battery voltage for very short instances. Since the bulb is an incandescent, it responds to average current. Therefore, a dim glow represents intermittent current flow such as pulses. Such pulses occur in the alternator output when one of the internal diodes is shorted. Either the diode assembly in the alternator must be replaced or a rebuilt alternator installed. An oscilloscope is needed to see these pulses, a voltmeter will not respond fast enough to detect them.

Sounds daft, but is the drive belt(s) in good order?

Regards,

Big Rich.
--
'86 245, B230A. 161k. Old 200s never die, they just live on in other cars.

I had the same problem and I just finished re-routing the alternator charge warning light wire from the alternator to the harness plug. This solved my problem. use some 16 ga wire and run it from the spade terminal on tha back of the alternator along the passanger side of the engine compartment, up to the fire wall and then I spliced it into the correct wire at the connector. All better!

Does the alternator ligt pulse when you turn on the directional indicator???

Take the voltage regulator off and check it out. If you've got an internal regulator this is really easy.. two screws and it'll be really self evident... especially since you don't have a turbo (i.e. you have plenty of space by the exhaust manifold). Disconnect the battery first tho.

- alex

'85 244 Turbo

With the voltage regulator out, look at the brushes. If they are under 5mm long, get a new unit which includes the internal voltage regulator. If the brushes are OK, you may have a failing diode. Also, be sure the alternator is grounded to the block.

Hope this helps.

Good Luck

Bob

:>)