Re: [AMC-List] Weird charging system problems

[Tom Jennings <tomj@xxxxxxx>]

re: crazy alternator:

assuming the parts are good, it's wiring; likely ground problems as Mark
and others pointed out.

Electrical connections need as much care and feeding as the rest of the
engine. Loose screws, frayed wires, non-shiny connectors, loose
fast-ons, etc, any one could do it.

Some of those Moto regulators ground themselves by the case to the
fender; unbolt it, sand the metal bare and shiny on the fender and reg
case, make sure it's flat, use the right screw and make it tight. If
it's not TIGHT TIGHT it will fail, or worse, be erratic, which seems to
be what you have.

If your battery cables are not in LIKE NEW condition, replace them. Wire
brush the posts, apply grease, tighten. The grease keeps out air and
water, and the pressure from the properly tightened bolt will squeeze it
out between the metal-to-metal portion and make a good connection.

The engine block needs to be extremely well grounded to the chasis. Buy
a new cable if necessary. That ground strap carries the entire
electrical load of averything in the car except what's bolted to the
block (eg. not starter, alternator, ignition and some others).

Some AMCs have a weird ground wire from the dash that seems to come back
into the engine compartment and bolts to the firewall. Never owned one
of those, couldn't tell you where it is!

THe alternator body is grounded through the bracket bolts; it seems
unlikely that it's not grounded, even if loose.

One bad diode in the alternator will generally just make it not charge
well, such as at idle; depending on the diode, it could cause battery
drain when the car is off. HOwever, at reasonable RPMs it should charge
reasonably.

Short of a voltmeter and analysis, my favorite alternator/generator test
is this:

* Engine running, low/normal idle, headlights on. Note brightness.

* rev engine to 2000 - 3000; headlights should get brighter.

If above doesn't happen, charging system isn't working. 

The reason the test is always valid is, due to chemistry and physics a
charged 12V lead/acid battery droops to 12 - 13 volts; a working
charging system brings the battery up to 14.4 to 14.7 volts; you can
easily see the increase in brightness due to raised voltage (brightness
increases by the square of the power increase).

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