"Does the fact that the charge warning light not come on sound like a plausable reason for my charging problems?"

Absolutely. When you pulled the cluster back you probbably loosened a small, 3-wire, right-angle connector that pushes onto the back of the speedometer.

In the picture below, note the brownish vertical strip on the left side of the speedo — just to the right of the circled double spade terminals. That strip is actually a printed circuit board where the 3-wire connector fits on. (I thought it had a white plastic latch to secure it, but it may be missing.)

The wire colors are:

• Red/Black +12V input to cluster
• Black speed sensor wire
• Blue speed sensor wire.

That connector brings in the +12V to power the normal (not ABS or SRS) warning lights. The current thru that Batt light (and 3 others) goes to ground thru the alternator, and is required to "pre-exite" the charging circuits.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.