Could anyone help diagnose this problem. We have a 76 beetle and the charging light is not going out until above 3500 RPM's . It used to go out about 1000 RPM's. The multimeter reads 11.75v when the light is on and 12.95 when the light is off. Any ideas ?

how are the bushes in the unit.

It was rebuilt 6 months ago so they should be ok but havent checked yet.

is the wiring right on the back of the alt,no half broken wires

Can we clear a couple of things

You say alternator problems and 1976 beetle.

A 1976 beetle "should" have an internal regulator alternator.

Brushes are on generators

If you have a internal reg beetle i think you will need to swap units as there isnt anything you can do.

Hi,
Internal or external Regulator Alternators both have brushes....
The external regulator is the weak part if You have one of those type of Alternators...

The internal Regulator Alternators have [usually] only two connections...
One heavy wire for the power to go to the Battery...
and the small lead to go to the bulb in the dash/speedometer....
The light bulb is needed to excite the alternator into producing electricity....
My Volt meter in My dash reads around 14 volts most of the time I'm driving....
under 13 volts means You have a problem....
The light bulb in the dash should go out as soon as You rev the engine or sooner...

It sounds like Your Alternator needs an overhaul at an auto electrician... get a quote first...
If its brushes or diodes , it shouldn't be expensive...
but if a field coil etc has burnt out it will cost more...

with the voltages You quoted, something isn't working correctly....
Its usually only brushes or diodes or the regulator that may give trouble.....

Best of Luck

Lee

http://community.webshots.com/user/vw68autobug 

Hmmmm............. gunna have to pull an alternator apart one day and have a good look.

"There are two bearings, one at each end, and two brushes which ride on "slip rings"; on the spinning part. There should be a brush-block on the side or top which may be removable so you could see the state of the brushes (the old style generator brushes are replacable in the car, but I haven't had a REAL close look at the alternator). Alternator brushes wear much slower that generator brushes, so it may just have a slow deterioration of these. If they are worn, also check that the slip rings aren't too worn down into "valleys" where the brushes ride. If this happens the alternator would definitely need to go to an overhaul place to have the rings machined or replaced so new brushes will ride properly."

Damn that Rob and dave is a good site :blush

how do you think they get the power out of the rotating machinery other than a slip ring

I thought it was just induced fields

Like how a motor can generate - no brushes there

they are there.