Who knows alternators? Looking for authoritative info about turning it ON or OFF

[JanGeo]

There should be a idot light wire also so don't get that one confused.

[MetroMPG]

Yup, there's also an idiot light wire in the schematic.

[skewbe]

Originally Posted by MetroMPG

Cool, thanks.

It also shows: no fuse in the alternator circuit

on page 21, ( of the 1997 diagrams, page 22 of the 98+ diagrams) there is a fuse in the lower right (fuse 21 , 15 amps)

Your alternator should never "boot up" if that fuse is removed. Also a convenient place to jam a couple switch leads into if so (with an inline fuse if you like). No guarantees that there isn't more downstream of that fuse than represented in the picture of course.

Looks like your DRLs will be out too, but that's probably just fine with the alternator off.

[MetroMPG]

Originally Posted by skewbe

on page 21, ( of the 1997 diagrams, page 22 of the 98+ diagrams) there is a fuse in the lower right (fuse 21 , 15 amps)
...
No guarantees that there isn't more downstream of that fuse than represented in the picture of course.

I assumed that fuse was for the general ignition circuit, and nothing would boot up without it. Maybe it's not. Easy enough to test though... I may just try pulling it today and see what happens.

I discovered the DRLs were part of the alternator circuit from going alternator-less last summer. It was a nice surprise to see some engineer had thought: "better kill those lights if the alternator fails... " to give the poor saps with dead alternators a little more driving time to get help.

[MetroMPG]

So the two small wires (from the ignition and idiot light) connect to the alternator with a quick release type connector. I had a look a little while ago when I went out to plug in the block heater.

They're not super easy to get at (cabin switch would definitely be preferable), but I unplugged them for my next trip, in an hour or so.

Are we sure this isn't going to harm the alternator?

Will report back.

[MetroMPG]

Well, wouldn't have predicted this: with the idiot light & ignition wire disconnected, the alternator still worked.

The SG reported high 13.x / low 14.x volts within a few seconds of starting the engine. I drove for maybe 1 minute, then stopped and plugged it back in (unexpected results = didn't want to keep operating it like that not knowing the potential consequences).

Afterwards I tried again in the driveway: disconnected the plug from the alternator, started the engine. It ran @ battery voltage for perhaps 1 or 2 seconds then the alternator perceptibly "kicked in" (could hear the abrupt load on the engine) and voltage went up.

Stopped the engine, reconnected the plug & restarted. Alternator was working immediately after the start.

Pondering this...

[MetroMPG]

It has been suggested on the EVDL that the resistance of the idiot light circuit may be part of the control to the voltage regulator.

Maybe I need to leave it attached, and just remove the ignition wire. May try this later.

[skewbe]

Originally Posted by MetroMPG

I assumed that fuse was for the general ignition circuit, and nothing would boot up without it.

LOL, I cracked open the factory service manual, yes that must source the ignition switch.

I can't fully explain why it boots up when disconnected, except to say the internal regulator allowed it. You essentially have a single wire alternator there in that mode

[MetroMPG]

Well, it's still not warm enough to be futzing around with cars outside.

Spent about 25 minutes trying to find the blk/whi wire from the ignition (from the fuse block inside the car) to the alternator, and I couldn't. I did find 2 blk/whi wires, but neither was the one (when tested for continuity).

I can't fully explain why it boots up when disconnected, except to say the internal regulator allowed it.

Well, looking at the schematic in my service manual, the internal regulator has 3 inputs: the ignition & idiot light wires we already know about, and internally the regulator is also connected to the fat battery (+) wire. So that explains how it can regulate with the other two removed.

It's looking like I'll also have to switch the fat battery (+) wire to completely isolate the alternator.

Why did they make it so hard for this to fail?

[MetroMPG]

Here's my service manual's charging schematic. Maybe too blurry to be useful, but it shows the internals of the alternator (labeled "generator") with the batt (+) wire split off to also connect with the IC Regulator.