Alternator rebuilt. Rebuilder ran 100 amps against alternator,on a device he has, to see if it would fail. No failure. Problem only occurs with headlights on.
Installed new battery today because I had discharged the old one by leaving the dome light on 3 days. Had problem recharging it. Rebuild was completed just after that.
Fan belt is tight.

On going problem after rebuild. I began my test drive down a road at 30 mph, with headlights on for several miles & voltage drops 14.3 v to 12.9.. Stayed there . When I slowed down for couple of miles voltage returned to 14.3. If I turn off the headlights, today, it eventually climbed back to 14.3. On the highway at 55 mph, it then dropped to about 12.9.. Stayed that way until reached home .
I grabbed my multi-meter & infrared heat test unit. Temps on the alt pulley & shaft were 190 & 200 respectively. Alternator temp was 175 *f. Voltage output rose very slowly as alt cooled, from 12.9 to 14.3+. With headlights off, alt cooled to, on the pulley & shaft at 170 & 175 respectively.
I waited 10 minutes & tuned the headlight on. Voltage stayed constant at over 14 for 10 minutes, at engine idle. I Shutdown.
When the headlights are turned on u can hear the alternator engage to product the power.

I can see no reason as to what could be causing such a high amperage draw as to heat the alternator to these high temps. I believe the alternator is breaking down due to excessive heating...
Suggestions or ideas.
I may try and locate 12si with 94 amps

 

What problems?

Not Likely.

Alternator will be the same as under hood temps. 180-220'ish
I'd look for bad connections at the alternator output post, the positive connections at the starter, and engine ground to battery.
Make sure the alternator exciter wire is working.
If those are good your rebuilder is not as good as he thinks he is, suspect a bad internal regulator. Take it somewhere else to have it tested.

 

I may have solved my problem.
I added a ground strap from engine to chassis to see if that would make a difference (I had to do in my 1972 Buick GS way back as it was missing)
Here are the volt readings at various times in my 20 mile run.
1) engine off = 12.66 lights off
2) at idle = 14.6 lights off
3) after a few miles = 14.6 lights off
4) lights on = 14.36 & alt temp = 160 tops
5) after 20 miles on the road at various speeds back at home = 14.36 alt temp 160 tops
My next out of town long run is in a couple weeks, so I will cross my fingers & hope problem is solved!