Igntion cutting out under load

[mardak at cogeco.ca (Mark)]

Here's the symptoms (81 8v ABA/JH running CIS lambda):  feels like the
ignition is cutting out under load, with high alternator load (heater
fan on high, headlights on).  Happens when accelerating hard in mid to
upper rpm range.

No problems if accessories are off.  Recent rotor/cap/plugs/coil.

I'm thinking I either have a bad ground somewhere, or my alternator
isn't putting out enough juice to power the coil under load.  Any
suggestions where to start?  It's cold/rainy out, and I have to hire a
flatbed to get my car in my shop (loading dock height), so unless it's
major I'm going to freeze my ass off...

Mark.
80 S
81 S  2.0 ABA/JH/4K