Alternator light intermittent

Well, since no one else has responded, I’ll take a whirl. 
The dash light is not grounded.   It has +12  volts coming to it from the fuse panel on one side of the light and from the “D+” tab on the alternator (the small 1/4” tab next to the big red wire On the alternator) on the other side.   If any of those connectors on the alternator or dash light are dirty/corroded, it can cause what you’re seeing.   Try cleaning them up as best you can and see if that helps. 

Also, clean both battery cable clamps as well as the battery cable lug at the starter. 

gn

Did you check the voltage at both the alternator and the battery?

Two things: 

Firstly, if the voltage at the alternator output terminal is less than 13.8, engine running(and try revving it to see if voltage goes up, light should go out), your voltage regulator is either set too low, or on the way out. Replace it.

13.8 to 14.2 is perfect charging voltage, depending on battery condition, load, and rpms of course.

Check the voltage between ground(alternator case) and positive alternator terminal. Use a digital multimeter. Then check the voltage across the battery terminals, engine running. If the battery measures more than 0.1 volt less, more investigation is needed to see where you're losing the voltage. It could be a bad ground, bad crimp, corroded cable or end internally, bad positive or ground cable etc.....

What Danny P said x 2

@Impala posted:

 

...The ground strap from the transaxle to the chassis is solid....

You can't really be sure until you unbolt the connections, sand down to bare metal, and reconnect. They can be mechanically solid, but still not electrically connected. Corrosion is really good at hiding from us.

This goes for any connections in the battery/alternator/charging circuits. Always the first thing to check before you start replacing stuff.

I am on my 4th Alternator in 10 years. 3 Bosch and one knockoff because it was all that was available at the time. The knockoff lasted 3 months. The Bosch units seem to have a 3 year life cycle. In every case it was the failure of the internal voltage regulator. 

I'd be learning how to take it apart and swap the regulator. Or at least find an auto electric guy to swap it. I went through a couple on the Spyder until I had my local auto electric guy order me a good one from a reliable supplier.

It sounds to me like maybe you've got a bad or loose ground somewhere Noel. That would make a regulator go bad prematurely. I've had them go bad, but not 4 in 10 years.