I have a big problem.  On the '71, the charging system is acting all 
screwy.  For some reason, occasionally it works, and occasionally it 
doesn't.  

The Problem:

I was driving out to the Targhee Nat. Forest in Idaho last week.  
It's about 40 miles from my parent's house in Idaho Falls to 
Pallisaides, and the trip out went just fine.  It seems that on the 
return leg, however, after a little while, the alternator stopped 
putting out voltage to run the car.  For some reason the idiot light 
didn't come on, but the engine started missing badly, and after 
climbing the mother of all grades out of Swan Valley, I pulled over 
to check things out.  The engine wasn't hot, and the battery was 
very, very weak ( < 25% charge).  I figured the missing, etc was 
caused by incomplete combustion (low voltage) which probably fouled 
the plugs; no problem there.  We towed the bus back to my 
parent's house, a long, cold, scary (8' tow rope, lots of stop signs 
and country roads; glad I just replaced the rotors) ride.  Many 
thanks to my brother in law, Brian Christiensen for keeping me 
company.  When we got home, we replaced the alternator with a spare 
bosch (see below) I had on a Beetle engine, charged the battery, and 
installed an ammeter to take the place of the seemingly faulty 
Generator light.  I thought that would take care of things, but my Dad 
called last night to say that he took it to work on Monday (he 
drove it all last week w/o incident).  Apparently he went over a bump 
in the road, and the generator light came glaring on.  He was able to 
limp in to work with a dead battery, and a cool engine. AAARRRGH.  
Back to square one.

Specs:

The alternator is a Bosch internaly regulated unit, six 
months old.  The battery is an interstate with barely four months of 
use.  I had thought the problem was my old alternator/regulator 
(Motorolla), and swapped it out for the new Bosch last week.  The 
starter is new (like that has anything to do with anything).

My Thoughts/Queries:

1.  Ground straps:  Where are they; could they cause the problem?

2.  Generator light spookiness:  How could this figure in to 
    things?

3.  Could the alternator be messed up?

4.  Could the ammeter wiring be affecting things?  I used 12 ga wire 
    (the heaviest stuff I could find at night in Idaho Falls).

I've checked Muir and Bently.  This is more of an old wiring thing, I 
suspect, than anything that they would seem to have truck with.     

Any help at all would be greatly appreciated.  Thanks!

Shaun