I have been putting off the issue of dealing with the fact that my lights would dim on a cycle up and down ever so slightly ...usually independent of motor speed.... finally I ran the battery down... found the larger red wire going to the alternator had broken off the clip to the back of the alternator (by the way, I have replaced the unit within the last couple of years via autozone and recently had it checked by them .... it was charging as normal)

over time though, the alt light has come on ever so dimly...and finally recently it has proven itself to be on all the way... after fixing the broken wire.... the alt light went out...but then the car flattened the battery... I have been working on it today....then the alt lite stayed off but the other lites worked...now no lights work... I did reinstall a ground wire from the back of the alt (tapped off one of the screws holding the rectifier in place) and grounded it to the body of the car.

any help would be appreciated.

thanks

david

Well, this happened to me yesterday. The red wire stayed in place enough of the time to sort of make contact- I found it sparking against the terminal. Damn glad that it didn't hit the alternator case because that would be a fire!!! Fortunately it happened to me on the highway, one exit from where I work- drove there and right inside the shop, and went through my toolbox to find a good quality large gauge ring terminal.
I recommend that EVERYONE check closely the condition of the terminal on your alternator. I fixed mine before the alternator got damaged apparently- 12.47V when off, 14.35V when running.
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total

"tapped off one of the screws holding the rectifier in place"

On a much older car, I had a lousy connection to the regulator through its ground at the mounting screw. The symptom was no charging, but no warning lamp, and yes, lamp test worked. Caused it myself, by the way -- just turned the screw in another 1/2 turn.
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Art Benstein near Baltimore

the fact that all the warning lights are not working are making me think that it is something in addition to the altenator ... where are the diodes?

When you switch the key to pos II before starting the engine, the warning lights receive battery voltage through the ignition switch and a ground through the small red wire to the alternator that is not turning. You could test this by pulling the small red lead from the tab on the alternator and grounding it while someone looked at the lights.

When the car is running, the alternator raises the voltage on the red wire so the lights go out, unless they receive a ground from the function they are monitoring.

There are diodes in the alternator, rectifying the high current output, found on a large heat sink under the end cover. Also, if someone referred to them, there are steering diodes in the instrument cluster used to facilitate the warning light logic.

The diodes in the alternator are below this plate:

this is a rebuilt alternator from AutoZone, if the diodes went on it... would no grounding effect take place? ( I am thinking that when the "big" red wire broke off the Alt..that maybe it shorted the system?.. and I am still at a loss where the ground wire could have been... as I do remember "rigging" one when I replaced it last time) The replacement alternator did not have a very good grounding spot on it... today I backed out one of the screws holding the rectifier and attached the wire at that point...

the only reason that I haven't suspected the alternator immediately is the fact that I just had it checked a month ago at AutoZone (not that that says a lot!).. the alt has a lifetime warranty... so to do a switch would be only labor... and at 12 degrees outside... a bit of a pain.

also.... I had the problem previously with the lights cycling up and down on a constant base regardless of the engine speed..?

thanks

david

The alternator's ground is normally done to one of the four long bolts that run through the whole assembly, binding the end caps to the stator core. It is somewhere between an 8 and 10 gauge blue wire leading to one of the bolts mounting the alternator bracket, I think, in order to make up for the fact the unit is electrically isolated from ground by the rubber bushings. I figured you meant "regulator" when you said "rectifier", so I related my story about the symptoms of a missing regulator ground.

The "ground" that turns on the battery light when the alternator is still is made through the regulator and brushes for the rotor. There are 9 diodes inside the alternator, the six high-current diodes that do the main job of rectifying the charging current, and three diodes from the stator windings to provide the rotor current once the alternator is turning. That same voltage is seen by the red wire back to the instrument cluster, but not until the alternator is producing energy. The three small diodes (actually in one package) are facing the wrong direction to provide a ground for the battery light.

How did your test work out-- grounding the small red lead while looking at the cluster idiot lights?
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Art Benstein near Baltimore