Calling alternator experts

[yelcab1]

I have a 1990 engine with an alternator that is not charging, and it's not the alternator problem. There are only 3 wires going to it.

12V, checked that it connects to the starter and then the battery. Good.
GRD, checked that it see 0 ohms to the body, good.
Excitation terminal.

So what voltage should I see at the excitation terminal when the key is at "Start" position? 1/2/3/4 or 12V ?

[11BC2]

You should see roughly battery voltage at that wire

[yelcab1]

While the engine is cranking, I should see battery voltage at the excitation terminal?

[PeteKz]

I'm not sure about 1990 engines, but earlier engines relied on voltage supplied through the generator warning light to excite the field. Did you replace your gen. light with an LED? Is it burned out?

[yelcab1]

Yes, the excitation terminal is fed ...

Igntion On wire (12v with key on)
to Positive side of the Gen light
LED light (since removed and replaced with simple bulb) (on a side note, where do I get one of the LED thing?)
to negative side of the Gen light
to the Excitation terminal of the alternator

At key off, the E terminal of the alternator is close to ground
At key on, the E terminal of the alternator is less than 1V and the G light on the dash is on.

What should it be while cranking in order to excite the alternator? 1V, 5V, 12v?

[john walker's workshop]

Clock issue?

[mysocal911]

Originally Posted by yelcab1

I have a 1990 engine with an alternator that is not charging, and it's not the alternator problem. There are only 3 wires going to it.

12V, checked that it connects to the starter and then the battery. Good.
GRD, checked that it see 0 ohms to the body, good.
Excitation terminal.

So what voltage should I see at the excitation terminal when the key is at "Start" position? 1/2/3/4 or 12V ?

To "start" the alt charging, the terminal current needs to be greater than 100ma via the bulb.

[yelcab1]

Originally Posted by john walker's workshop

Clock issue?

Please explain?

[yelcab1]

Originally Posted by mysocal911

To "start" the alt charging, the terminal current needs to be greater than 100ma via the bulb.

So if the bulb is 50-60 ohms, that would be enough.?

[john walker's workshop]

Many circuits go through the clock. Does the charging light in the clock light up with the key on?

[yelcab1]

Well, it's a 71 body with a '90 3.6L engine. The gauges are not original to the 71 especially the speedo and tacho. The charging light was changed to an LED which I took out and replaced with a regular incandescent bulb. I am not sure if the clock is doing much if anything.

[john walker's workshop]

Assumed it was a 964. You didn't say '71 body.

[yelcab1]

Well, OK. It turned out to be a very bad battery that caused everything... including no alternator excite ...

All is now well.